FMA Direct : LiPo Handbook

Lithium Polymer batteries are a new generation portable electric power source. They are different from other batteries used for RC. In 1959, when Fred Marks became involved in RC, only carbon zinc batteries were available to RC. Lead-acid batteries were used with a converter to generate 180V for the tubes used in transmitters, but all else was done with carbon zinc batteries.

The first time anything other than carbon zinc was used in RC was when the great Walt Good came to a meet in the early 1960s with some extraordinary cells he had obtained from Johns Hopkins Applied Physics Lab where he worked. The small Silver Cadmium cells were of great interest, but far out of reach of the average modeler.

Surplus wet Nickel Cadmium cells began to appear from the Nike missile program (they had to be replaced periodically) and found good use as glow plug lighters. In 1962, Fred obtained his first NiCd button cells from the ABC Battery Company. In due time, cylindrical NiCd cells came on the market with General Electric and Gulton as the first mass producers. It wasn’t long until the Japanese acquired the technology and rapidly drove down the price of NiCds.

NiCd technology has seen steady if slow growth over the ensuing 40 years. NiMH became a new technology only in the early nineties and has grown a bit faster than NiCd. The primary attraction for NiMH was lighter weight and better environmental characteristics.

About 1980, Lithium Ion (Li Ion) cells began to be used for light duty, lightweight applications. Li Ion cells began to be modified for RC from retired cell phones and surplus sources only about four years ago. Li Ion cells can tolerate only modest discharge rates but found some use in powering electric airplanes.

Lithium Polymer (Li Po) cells began to see use in 2001 in a small way. The “small way” was primarily in the form of the Kokam Engineering Co., Ltd. 145 mAh cell.

A brief history of the development of Li Po technology follows:

Early in 1980, Motorola and Sony decided to apply lithium ion technology to the mobile phone to reduce weight and improve energy density, even though there were safety issues as there are now. They developed a safety module, the so-called PCM (protection circuit module). Up to now there have been few accidents from Li Ion.

Meanwhile, the Bellcore Lab in San Diego announced that they had developed the lithium polymer battery to increase energy density and safety by using a plastic pouch packaging/stacking method (different than Kokam’s system) using an ion conductive separator named PVDF (polyvinyldifluoride) which has good binding characteristics at 100° C.

Sony, Toshiba, Panasonic, Samsung, Saft, Varta, Valence, Ultra-life, Polystar and perhaps 30 companies bought licenses to commercialize the Bellcore technology during the period since. No one was successful due to the difficulties of mass production technology when using this technology. Everybody gave up or went bankrupt. Sony started a new method which modified conventional technology with PVDF material only, but closely related to winding technology. With this material (PVDF), it is very difficult to achieve high power drain due to the limitations of the ion conductive material itself. Wound cells cannot achieve high discharge rates because of high current drain from the anode tab. Winding has a longer electrode which increases the internal resistance at high current draw.

Kokam, too, evaluated Bellcore technology as an alternative, but realized that it is not a practical technology for commercialization due to the processing difficulty. Thus, Kokam decided to develop new technology with assistance from the Korean government agency named KIST (Korea Institute of Science and Technology). A new system was invented system that permits Kokam to make the battery easier with significant improvement over Li Ion and providing better safety. Kokam acquired patents world - wide and started to design the full process and equipment suitable for mass producing Kokam cells. German and Chinese companies licensed Kokam technologies.

With the Kokam technology, we have successfully created the first 20C discharge rate commercial Li Po battery

In June 2002, FMA, Inc. and Kokam Engineering Co., Ltd. signed an agreement for FMA to serve as the agent for Kokam in North and South America. In October 2002, FMA, Inc. began actively shipping Kokam Lithium Polymer (Li Po) cells. As of this writing, over 2,000,000 cells are being used in RC models.

At this time, FMA Direct has been actively promoting the use of Li Po cells and packs for three years with gratifying results. In the past three years, Li Po technology has advanced farther than NiCd technology advanced in nearly forty years. In 2002, the standard Kokam cell was capable of continuous operation at three to four times the multiple of capacity (3 to 4C) with 5C as the upper limit. In the past two years, FMA/Kokam has introduced, and FMA now has on the market, cells capable of sustaining up to 20C with loss of but a few percent capacity and with the capability to withstand pulses of current of < one second duration at up to 40C . Detailed performance data are available as Data Sheets in the FMA Li Po Compendium. During 2004, FMA/Kokam reduced Li Po cost by one-third.

From the beginning of its involvement with Li Po technology, FMA has anticipated the need for a system of Li Po components. Several factors influenced this approach:

· Li Po batteries require different chargers than other chemistries.

· The 3.7V cell output requires that packs and ESCs must be designed and sized differently.

· It was desired to make it as easy as possible for the NiCd/NiMH user to make the transition to Li Po.

· Li Po cells have unique safety and operating rules.

· Over the past four years, FMA has addressed and optimized all aspects of successful use of Li Po batteries.

By providing all the elements needed (below), FMA hopes that Li Po will continue the rapid rate of acceptance and success seen to date. We truly believe that glow engine power will be largely replaced by Li Po power over the next few years.

See all products needed to make you successful with Li Po batteries at www.fmadirect.com

Balance charge packs ( Scorpion, BalancePro, CellPro )

Standard packs

Car pack with built in cut - off

Scorpion car charger and pack system

Charge protection modules for use with any approved Li Po charger protect against over voltage for 1 to 6S

Discharge protection modules protect against unde voltage for 1 to 6S. Can be daisy chained in sets of six

SKYVOLT 6S Cell balance charger maintains perfect match in cells for packs up to 6S

BalancePro cell balancing charger for 2S. Can charge parallel 2S packs up to 10 amps

Economical 1S and 2S chargers for the smaller Li Pos

LIPO 502: Charge up to 4S packs with auto cell count that never misses

AVC 1 AIR: Salvage any ESC for use with Li Po packs

Getting interference from high current power systems? 4CH OPTOISOLATOR stops that.

Need to drive big servos at up to 10 amps? 10 AMP REGULATOR

Connector modules permit parallel or series connection for maximum flexibility

Microameter inserts in battery line to ESC so you really know what the current drain is. No more guessing!

Combine our on-board microammeter with our on-board recorder to measure up to 100 amps

Servos in many sizes including the top digital servo made

All FMA receivers feature dual conversion and Digital Signal Recognition

Building Li Po packs

The basic cell

Using Li Po cells was challenging for early users, and only the most persistent did what it took to use them. The first cells had only bare tabs that were thin and fragile, and one tab was aluminum that required special solder and techniques.

The first improvement was to weld a nickel tab to the aluminum tab that, in turn, could be soldered. The next improvement was incorporating a small pc terminal board on each cell that made soldering as easy as for any cell with terminal lugs. Such cells are available still for certified pack builders who purchase in quantity. *

Text Box:

*Note: Home construction of packs using bare tabs is not encouraged because poor technique can damage the plastic envelope where the tabs exit the cell. This can shorten cell life. Cells and packs should be manufactured by a professional pack assembly house. Assembly by end users is not covered by warranty.

Wiring an individual cell

Some assemblers want to design custom modules using individual cells with the terminal blocks. This approach starts with the standard Kokam cells, identified by the “T” suffix; e.g., 145T.

How cells are connected

Series connected cells

In a series connected pack, the negative terminal of one cell connects to the positive terminal of the next cell. Output voltage is taken from the first and last cells in the chain. In this example, four cells are connected in series. This is called a 4s pack.

A series connected pack is used to supply more voltage than a single cell. The nominal output voltage from the example 4s pack is 4 x 3.7V = 14.8V.

Note: When connecting cells in series:

n All cells must be the same capacity (mAh).

n All cells must be in the same state of charge.

Parallel connected cells

In a parallel - connected pack, all the cells’ positive terminals are connected, and all the cells’ negative terminals are connected. In this example, four cells are connected in parallel. This is called a 4p pack.

A parallel - connected pack is used to supply more current than a single cell. The output capacity from the example 4p pack is four times the individual cell capacity. If the pack were made with KOK145 (145mAh capacity) cells, the pack’s capacity would be
4 x 145mAh = 580mAh. Its nominal output voltage would be the same as a single cell, 3.7V.

Note: When connecting cells in parallel:

n All cells must be the same capacity (mAh).

n All cells must be in the same state of charge.

Series/parallel connected packs

Text Box: Many RC applications require both higher voltage and higher current. Li Po packs can be assembled with both series and parallel connections.

The drawing to the right shows a 2s4p pack. It starts with four pairs of cells connected in series. Those four pairs are then connected in parallel. The pack’s output voltage would be 2 x 3.7V = 7.4V. It’s capacity would be four times the capacity of the individual cells.

The drawing below shows a 4s2p pack. It starts with two sets of four cells connected in series. Those two sets are then connected in parallel. The pack’s output voltage would be
4 x 3.7V = 14.8V. Its capacity would be two times the capacity of the individual cells.

Note: When connecting cells in series/parallel packs:

n All cells must be the same capacity (mAh).

n All cells must be in the same state of charge.

How modular packs are manufactured

Kokam modular packs are assembled as shown below. The pc boards work extremely well and stiffen up the end of the pack. The pc board and, thus, the cell terminals are accessible. If heat shrink has covered a connection, it can be accessed with a sharp tool or by careful removal of a small square of heat shrink material.

NOTE: ALL FMA/KOKAM PACKS HAVE BEEN CONSTRUCTED AS SHOWN ABOVE UNTIL JULY 2005. STARTING IN JUNE 2005 UNITIZED PACKS ARE BEING INTRODUCED AS ILLUSTRATED IN SECTIONS THAT FOLLOW.
The Li Po modular pack connection system

Two key types of components provide a foundation for the system approach to Li Po power:

n Preassembled Li Po packs with attached wires and plugs.

n Connector modules that enable packs to be connected in almost any configuration.

With the Li Po pack system, users can quickly and easily build custom power systems with increased voltage, increased capacity or both. NOTE: It is the user’s choice to use FMA modular packs for flexibility or to use FMA unitized packs for simplicity.

The photo below shows four preassembled packs plugged into a Parallel Connector Module. The Module is then attached to an ESC for powering an RC model.

Connector Module Wires from ESC ESC

Wires preattached to packs

Four preassembled packs

Note: When assembling a multi-pack system with Connector Modules:

n All packs must be the same capacity (mAh) and voltage.

n All packs must be in the same state of charge.

Connector Modules are available in three sizes, with corresponding connectors, to handle a variety of power requirements:

n For high power applications:

n For moderate power applications:

n For low power applications:

The Connector Modules are made in series and parallel configurations with five connectors. Lines of tiny holes allow you to cut or snap off sections you don’t need (removed sections are fully functional). Modules can be cascaded; that is, several modules can be plugged into another module, which can be plugged into another module, and so on.

These examples show how various configurations can be built very quickly:

n Needed: a 2s3p pack (three parallel-connected packs of 2 cells in series). Solution: plug three preassembled 2s packs into a Parallel Connector Module.

n Needed: a 4s3p pack (three parallel-connected packs of 4 cells in series). Solution: plug two 2s packs into a Series Module; create two more assemblies just like it; plug the three assemblies into a Parallel Module.

Here’s a real-life example: Greg Covey built a 3s4p pack for his Wipa Firecat using the Kokam USA Connector Modules. Says Greg: “The 3s4p Kokam 1200HC pack tripled my flight time while being 5oz lighter than the 10-cell CP1700 NiCd pack.” Four 3s packs plug into a Parallel Module to make the 3s4p pack. You can even change pack configurations between flights. The CP1700 pack is 1700 mAh and weighs 19 oz. The total capacity of the Li Po pack is 4800 mAh and weight is 14 oz. The NiCd provides about 7 minutes flight time and the Li Po pack delivers about 21 minutes.

Building a modular Kokam Li Po “Super Pack”

This section is based on information and photos contributed by Greg Covey.

This section describes one way to create a 4s5p “Super Pack” of Kokam 1500HD cells that provides awesome power and duration! The 7500mAh capacity pack can deliver 50 to 60amps continuous and up to 75amps peak in short bursts.

A 2s5p or 3s5p configuration would be a simple plug-together assembly, as explained earlier in “The Li Po modular pack connection system.” The 4s5p configuration, on the other hand, requires a little re-wiring that can be done safely without disturbing the factory assembled pack.

One application for such a pack is to power the AXI 4120 External Rotor brushless motor... for very long flight times. Put two of these packs in series and you can power an AXI 5330 or Hacker B50XL motor.

Note: When interconnecting packs by soldering and when assembling a multi-pack system with Connector Modules:

n All packs must be the same capacity (mAh) and voltage.

n All packs must be in the same state of charge.

1. Start with two Kokam 2-cell 1500HD packs, in the same orientation, with the Kokam labels facing you.

2. Remove the labels securing the output leads (see above).

3. Stick the two packs together:

a. Place a strip of 1" wide servo tape over the label on one pack (see below). We’ll call this the rear pack.

b. Lift the front pack, align it over the rear pack, and press it into position.

4. With the front pack toward you, cut three wires as shown below.

5. Remove the Deans connector and its leads from the front pack.

6. Make the first solder connection, which connects the two packs:

a. Slide a piece of heat-shrink tubing over the short red wire on the rear pack.

b. Solder the black wire on the front pack to the short red wire on the rear pack, as shown here.

7. Make the second solder connection, which completes the circuit to the connector:

a. Slide a piece of heat-shrink tubing onto the red wire on the rear pack.

b. Solder the red wire on the front pack to the long red wire on the rear pack, as shown here:

8. You now have a 4s pack. Check the voltage at the connector; it should be about 14.8V if the cells are charged.

9. If the voltage is correct, slide the heat-shrink tubings over your solder connections and shrink them down.

10. Cover the pack with a piece of large heat-shrink tubing.

Wrap the pack with tape (for example, filament tape or packing tape).

11. Repeat steps 1 through 10 to build a total of five packs.

12. Plug the packs into a Kokam CMP-HC 5 (parallel) Connector Module.

13. Wrap duct tape around the Connector Module to prevent it from shorting.

14. You can tape the packs together. However, it is often advantageous to keep the packs separate so they can be inserted and arranged in the fuselage.

Tip: Use similar techniques to make 5s (2s + 3s, 18.5V) and 6s (3s + 3s, 22.2V) “super packs.”

CAUTION: The modular pack is a viable, safe way to use Li Po cells. It is very important to arrange access to the terminals of each cell so that cell balance can be checked occasionally using a Digital Voltmeter (DVM).

Unitized packs

SKYVOLT Application Examples

3. UltraRC 2-meter FAI Pattern Plane

The new SKYVOLT packs were used in an UltraRC Icepoint e-conversion. The 4-cell 3.2AH Kokam packs are pre-wired to a special connector so that each cell can be monitored during charge and discharge for optimal safety, longevity, and investment security. The SKYVOLT packs are used in conjunction with Protection Modules, one for charge and one for discharge. This new approach in Lithium cell safety and protection will be available around August/September 2005 from FMA Direct.

The Cell Pro 6s Discharge Protection Module (DPM) can monitor up to a 6s SKYVOLT pack to provide a warning when the voltage gets low and use any ESC to pulse the throttle signal to the motor to alert the pilot that it is time to land. There are two dip switches on the DPM but Switch #1 currently has no function. The units will work out of the box without doing any setup, but they perform optimally when you tell the units which way low throttle is using Switch #2 and use the learning procedure mentioned in the manual.

Note that two DPMs can be daisy-chained for up to 12s configurations.

The Cell Pro Charge Protection Module (CPM) is used with any Lithium charger to monitor individual cell voltages and disconnect the charger when the first cell reaches 4.2V. This extends pack life by preventing overcharging. Note that this does not balance all the cells in the pack; only the SKYVOLT Charger (not shown) provides true cell balancing during a charge.

Here is the SKYVOLT system installed in the Icepoint. The packs are mounted as before but they now connect to the Cell Pro 6s Discharge Protection Module (DPM) instead of directly to the ESC. The ESC control line is then routed through the DPM to control the motor shutoff. Since everything is mounted with Velcro, I can easily swap back to my non-SKYVOLT packs and continue flying. The ESC simply reconnects as normal to the receiver.

Setup was easy since everything was plug-n-play. The DIP switch #2 is enabled the first time to learn the off position of your transmitter so that the DPM can properly pulse the motor when the first cell goes below 2.55V under heavy load. Note that the DPM can both monitor and alter the throttle signal so it knows when the motor is at or near full throttle and it can softly warn the pilot that the batteries are low without an abrupt motor shutdown.

The optional LED/Speaker module appears to be quite useful as it relays visible and audible problems. If one accidentally leaves the battery connected for an hour with the transmitter off, the audible alert will let you know about it. The LED/Speaker module has many other alert features like checking to see if all the batteries are properly charged and testing for “brown – out” conditions that may mean a loose connection.

For more details on the Icepoint conversion to electric power, go here.

4. Fun World EP 3D Plane

The Fun World EP 50" 3D plane from World Models was recently retrofitted with a new 3-cell SKYVOLT 3.2AH pack and Cell Pro Discharge Protection Module (DPM). The SKYVOLT pack provides a 20C discharge rate and 3C (20 minute) charge rate using the highest technology Lithium cell protection ever seen in the R/C market. The SKYVOLT cell balancing charger (available in August/September 2005) and discharge protection circuitry combined with Kokam SHD type cells deliver the highest rates ever seen in R/C to provide more power and more flying time than any other Lithium technology system.

The SKYVOLT system will be for 2s-6s packs in which two systems can be connected in series for up to 12s setups. The 2s version of this system is known as the BalancePro for R/C airplanes and Scorpion for R/C cars. These 2s systems are available now and will be discussed next.

Balance Pro and Scorpion for the Two Cell Packs

1. Balance Pro is a logical spin-off from the popular Scorpion electric car racing system. Scorpion was used to develop the cell balance concept and has been in development for two years. Balance Pro is the airplane version that applies to every two-cell pack in use today. The function and use is the same as for SKYVOLT.

2. The accessory items for Balance Pro are simpler than for SKYVOLT. The charger is for two cells. The AVC 1 AIR can be used as the cut-off although any of our FMA speed controls can be set to use as the cut-off. Cell unbalance is less likely with two cells. Having the two cells charged to exact balance each charge suffices. Tthere is no need for a balancing cut-off device except for AVC 1 AIR.

FMA’s Balance Pro 2s Charger is part of a revolutionary new Li Po battery and charge system for R/C aircraft. In essence, it is very similar to the 2s Scorpion system for R/C cars. With a variable charge rate of 0.5amps to 10amps, the charger brings Balance Pro 2s packs to 90% of capacity in as little as 20 minutes. FMA’s Safe Charge Connector is a key part of the system. The connector enables the charger to monitor individual cells and independently charge each cell to its optimum level. Charge protection dramatically improves pack performance, pack life and charging safety. All Balance Pro packs from FMA come standard with the Safe Charge Connector. The Balance Pro charger may be used to charge only FMA's new Balance Pro 2S (7.4V) Li Po packs in capacities ranging from 1250 mAh to 6400 mAh.

At 7.4 volts, a single FMA BalancePro pack may be used in any application that requires a 2s Lithium pack for R/C aircraft. Further, you can place multiple BalancePro packs in series to obtain higher output voltages. Since the BalancePro charger can safely recharge a BalancePro pack at 3C (or 20 minutes), you can still charge three packs in the normal 60 minutes time of most other Lithium packs. Alternatively, you can use separate BalancePro chargers to keep the pack charge time down to only 20 minutes.

BalancePro Application Examples

1. Space Scooter Hop-up with BalancePro

As a performance hop-up, the new BalancePro technology from FMA Direct will super- charge the Multiplex Space Scooter by providing more power, less flying weight, and tripling the flight time!

Compared to the stock 5.5oz 7-cell, 600mAh NiCd pack, the 2-cell BalancePro 2000mAh Lithium pack weighs 1.2oz less and has 3.3 times the capacity! Since the BalancePro voltage-under-load is higher than the stock NiCd pack, you get an additional power boost on top of the lighter flying weight.

* BalancePro Pack provided 65w at 8.5amps
* Stock NiCd Pack provided 60w at 8.2amps

Note that the BalancePro discharge connector needed to be replaced with a Duratrax/Kyosho/Tamiya style connector at Tower Hobbies for compatibility

2. Multiplex Easystar Hop - up with BalancePro

The Multiplex Easystar from Hobby Lobby was easily upgraded to double the flight time over the stock 7-cell, 1100mAh NiMH pack using the BalancePro 2-cell, 2AH Lithium pack. The BalancePro provided slightly greater power than the stock pack and fit perfectly into the Easystar nose. The battery pack was held in place with a foam wedge.

To better facilitate longer flights, the ESC was mounted so that the top surface received direct air cooling. The BalancePro pack never gets warm due to the low 8amp maximum current draw and the motor cooling is already built into the Easystar fuselage. This system provides 10-15 minute flights while keeping all the components cool to increase longevity.

Cell Pro Balancing System (Coming mid-2005)

1. Cell Pro has been developed so that any FMA/Kokam pack in future, or retrofitted to packs sold the past three years, can benefit from cell balance control.

2. The Cell Pro pack can be any pack distributed by FMA/Kokam and equipped with the CellPro connector.

3. The system will include packs up to 4S.

4. Customer service for modification of FMA packs to the Cell Pro connector system may be offered at a modest charge depending on interest.

5. The block diagram and flow chart for Cell Pro closely parallels SKYVOLT and is not repeated here. The pack is defined by the CellPro connector. The RUN connector may be any of the standard FMA connectors or the connector of your choice. The CellPro connectors are very small and light - weight.

What Li Po packs can do

This beautiful giant scale model is powered by Li Po packs. It was entered in the 2003 U.S. Scale Masters meet and earned first place in Team Scale.

Chinese Turboprop Tu-4 AEW built by George Maiorana and flown by Dave Pinegar won first place in Team Scale at the 2003 U.S. Scale Masters meet. Li Po packs reduced weight from 29 lb 11 oz to 26 lb 2 oz, and doubled flight time.

George Maiorana, the builder, reports: “WOW says it all! Everything went excellent with the 4s3p 1500HC packs. The plane wowed Dave [Pinegar, the pilot], myself and everyone with its performance. Dave never had to use full throttle. 7.5 - minute flights took the packs to 15.4V with plenty to spare. It took 3.5 hours to recharge at that level (1/3 C). Without the Li Po packs, we would not have been able to compete with the plane. The flight schedule would have been too long for the NiMH 3000.”

One convenience of the modular system is that the connectors carry only a proportionate share of the current. In the 4s3p packs that George built, the total current delivered is an average of 27 to 30 amps. However, the individual 3p legs carry only 10 amps, so lighter connectors could be used until the collection point is reached (the connector at the left and right ends). Bear in mind that George’s four packs drive four brushless motors turning 16 inch, four-bladed carbon fiber props. What a project!

Kokam Li Po packs are exceptionally flexible. They are equally at home in a giant scale airplane, a helicopter, a 3D aerobat, a park flyer or an indoor model. Please open the Li Po Gallery Section of the FMA web site to see a wide range of applications.

For starters, a whole series of conversions of a variety of models that normally are glow engine powered appear at the following links:

Hangar 9 33% Edge 540 uses a large 10s3p Kokam 6.3AH pack made from 30 Kokam 2.1AH cells.

Ultra RC Icepoint 2-meter FAI pattern plane uses a Skyvolt 8s 3.2AH system.

Vmar Easy 3D conversion uses a 4-cell Kokam (20C) 3.2AH pack

Graupner Extra 300S uses a 4s2p configuration of Kokam (15C) 2AH cells

Hangar 9 Corsair F4U uses a 6s4p pack of Kokam 1500mAh cells

Below are other examples of Kokam cells used in smaller electric planes.

Fliton Flubber uses Kokam 3-cell 1500mAh pack

Multiplex Magister uses a 3-cell Kokam (20C) 3.2AH pack for more power and longer flights

Great Planes Slinger wing uses a 3-cell Kokam 2AH pack for a power hop-up

Fun World EP from World Models uses a 4-cell Kokam (15C) 2AH pack

What goes in to design of FMA cells and packs

1. Advertising and promotion, by nature, gloss over performance data and highlight the “general wonderfulness” of the product.

2. Experience at FMA/Kokam is that the user should have the best data that can be made available so that he can make an intelligent choice.

3. The stumbling block is that many do not want to spend the time to educate themselves about the cells or develop an understanding of cell technology.

4. The result often is that the buyer looks for the lowest price and often buys something that can never do the job he wants. Hence the caveat: Buy cheap, buy twice. Worse yet, the buyer is scared away from Li Po technology because of a bad experience. That, we want to prevent.

5. Accordingly, please be patients and try to get as much out of this handbook as you can.

6. The battery products and accessories covered here are truly superior because they are based in true need as learned over the past three years of concentrated activity.

7. The basic characteristics of Li Po cells are charted on the next page. The key points to review are:

· Low internal resistance means less voltage depression, lower operating temperature and higher capacity retention under load.

· Lower temperature means longer life.

· Basic chemistry and cell design contribute greatly to longevity.

· The chemistry for 4^th generation Li Po cells provides much better safety than was available two years ago.

· New charge and discharge control technology makes FMA packs safer than any other factor.

· Notwithstanding, one must observe proper safety precautions since lithium can ignite under circumstances of abuse.