Electric Flight Specialist since

Electric Flight Specialist since 1999

Guide to Lithium Poly (Li-Po) battery use and care.

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Lithium batteries are the preferred power sources for most electric modellers, giving high discharge rates and high energy storage/weight ratio. However, correct use and charging are essential for safety and life cycle reasons hopefully the following paragraphs will help your understanding of lithium battery technology.
Charging/Safety IMPORTANT! Lithium batteries should be treated with respect. Until you are willing to follow all safety precautions, DO NOT use them. If your a type of person that prefers to push the limits of products, or be haphazard about following safety requirements. Lithium technology is not for you.
Lithium cells must be charged very differently than NiCad or NiMH. NEVER use a NiCad or NiMH only battery charger. Simple “plug and play” lithium compatible auto chargers are fine, but usually lack the facility to “see” what is happening. We recommend using a programmable charger with data display and options for the type of battery / cell you are using. Investment in this item will pay dividends, built in safety features will prevent user error and optimise your understanding your battery packs. PLEASE BE RESPONSIBLE when charging lithium batteries, as the user you are assuming responsibility for the safe use and operation of the battery. Here are a few MANDATORY guidelines for charging / using Li-Po batteries

1. Use only a charger approved for lithium batteries. If a programmable charger is used (with data display) ensure you select the correct settings. Battery type, capacity and charge rate will set charging parameters. You need to understand the significance of the settings.
2. Make certain that the correct cell count is set on your charger. Observe the charger display closely at the start of charge, ensure the correct cell count continues to be displayed. If you don't know how to do this, learn how to use the charger, or don't charge the batteries.
3. Use the battery pack balance plug. Invest in a battery monitor device to check cell voltages. Before you charge a new lithium pack, check the voltage of each cell and continue to do this after every tenth cycle. If the pack is unbalanced (individual cells not within 0.1volt of each other) perform a “balance” charge your charger instruction will explain how! Do not charge a pack with substantially out of balance cells on a normal charge (without the balance plug connected) as individual cell voltages can exceed the max voltage, this will destroy the cell and render the pack unusable or worse! If after every discharge the pack is unbalanced you have a faulty cell and the pack must be replaced.
4. NEVER charge batteries unattended. This is the number one reason for houses and cars being burned to a crisp by lithium fires.
5. Use a safe surface to charge your batteries. If they burst into flame no damage will occur. Vented fire safes, pyrex dishes with sand in the bottom, fireplaces, plant pots, are all good options.
6. DO NOT CHARGE AT MORE THAN 1C unless specifically authorized by the pack manufacturer. Latest specification packs, in some cases, can safely charged at greater than 1C, however the life of the pack may be compromised. As user you follow guidance, make the decisions and assume responsibility for the safe use of the battery.
7. DO NOT puncture a cell, ever. If a cell balloons, quickly place it in a fire safe place, especially if you were charging it when it ballooned. Leave for at least 2 hours before discharging the cell/pack slowly. This can be done by wiring a flashlight bulb of appropriate voltage (higher voltage is ok, lower voltage is not) up to your battery. When the light is completely off, dispose the battery safely.

8. If you crash or drop your battery the cells they may be damaged. The pack may look fine, but could be shorted inside. If you crash in ANY way, carefully remove the battery pack from the aircraft and watch it carefully for at least the next 20 min. A damaged battery that catches fire whilst driving home could result in an embarrassing insurance claim or worse!
9. Charge your batteries in an open ventilated area. If a battery does rupture or explode hazardous fumes and material will spew from the battery.
10. Keep a bucket of sand nearby when you are flying or charging batteries. This is a cost effective way to extinguish fires. This is very cheap and absolutely necessary.

11. Storage. Lithium batteries do not self discharge appreciably. A fully charged pack can be left for two or three weeks with no noticeable loss of charge. However it is not recommended to store packs fully charged for extended periods. Store in dry, cool conditions, at a nominal voltage of 3.7v per cell. Allow the battery to warm up to room temperature prior to charging.

12. It can happen to you, please do not think “it won't happen to me” and find yourself trying to rescue your kids from your burning house or car. This is serious advice.

If you are unsure about any aspect of charging / connecting / using lithium batteries seek guidance.

Some additional detail relating to the Lithium cells and batteries.
Lithium Poly / Lithium ion /Lithium Fe
Lithium batteries are safely used in Cell Phone, Laptops, PDA's, Hearing Aids, Power tools etc. These devices have battery management built into the respective chargers. Modellers need to act as the management device! Several types of Lithium cells are available to modellers. They have different nominal / charged voltages. Lithium Ion (Li-io nominal voltage 3.6v per cell) , Lithium-Poly (Li-Po nominal voltage of 3.7v per cell and Lithium Fe (Li-Fe PO4, nominal voltage 3-3.3v)
Voltage and Cell Count:
Lithium batteries act differently to NiCd or NiMH packs, Li-Po batteries are fully charged when each cell has a voltage of 4.2 volts (4.1 for Li-Ion, 3.6v Li-Fe). For simplicity we will talk about Li-Po packs in the following guidelines. Li-Po’s are fully discharged when each cell has a voltage of 3.0 volts. It is important not to discharge beyond this value.
Use of lithium compatible electronic speed control (ESC) is critical to the life of your batteries. Ensure that the low voltage cut off (LVC) of your ESC cuts out on or above a value equating to 3.0v per cell. Use the ESC's programming to set the LVC to 3.0 volts per cell ( hard cut off) or 3.3 volts per cell (soft cut off) You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC. If your ESC has an automatic lithium mode, use it. It will correctly sense the number of cells and set the auto cut off appropriately. In this situation you can appreciate the importance of using correctly balanced and fully charged packs!
Capacity rating explained.
All RC batteries are rated in milli Amp hours, so if a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps) it will be completely discharged in one hour. Think of 2000 being “C” in this case, how “fast” the battery can discharge it's (2000mAh stored charge) is generally quoted in multiples of “C” i.e 10C, 20C, 40C and by implication the discharge current is time related. For instance, if 1 C discharges the battery in 1 hour. 2 C discharges the battery in half an hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at This current capacity limitation (C rating) on how fast they can discharged is what you pay more for as the value rises!

Li-Po batteries are often used, wired in parallel. This increases the current capacity of the resultant pair of battery packs. Two individual cells or batteries wired positive to positive and negative to negative become like one cell or battery with double the capacity. If you have 2 2000mAh cells or packs connected in parallel then the result is the same as 1 4000mAh cell or pack. This 4000mAh cell has the same C rating as the original 2000mAh cells did but discharge current is divided between the cells / packs. . Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method can be used to obtain high current cost effectively, without buying expensive “high C rated” packs.
When battery packs are used in series and parallel a naming convention is adopted that allows you to decipher how many cells are in parallel and how many are in series. This is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. Voltage would be 11.1v (3S nominal) but capacity would be 8400 mAH. Applying the “c“ rating definition from above, even economy cells of 10C rating could allow currents of 84 Amps!
Which battery should you buy?
It’s your choice! However beware of marketing hype. Manufacturers are constantly trying to one up one another. Graphs illustrating how low the voltage of the cell drops at various load currents, will give you a metric to compare similar size/weight batteries. If graphs aren't your thing, simply look at what people are using in successful setups similar to your application. Long flight times and lots of power from airplane X, with power system Y, and battery Z points you in the right direction.
It pays to learn something about Watts, Volts, and Amps and crucially, the effect that different component specification can have on these values. Understanding these relationships is desirable. Use of a Watt meter is highly recommended to achieve best performance, without risking damage to the motor / controller / battery package.
High “C rated” packs will probably give a more stable voltage when discharged at high current but you may be paying for something you do not need! We recommend using a battery at a around 80% of it’s max rated constant discharge current. This leaves a little headroom whilst ensuring good performance.
6. Dealing with temperature.
Lithium batteries like heat, but not too much! In the winter time, keep your batteries from the cold as much as possible. Leave them in the car until required. At the same time don't let them heat up too much. Try to keep your batteries from reaching 160F during or after use. This will prolong the life of the cells