Lithium Polymer Battery Frequently Asked Questions:

1. What is this 'balancing' business?

Each cell of a Lithium Polymer battery has a nominal voltage of 3.7v, and they are connected in series. This results in a 2-cell Lipo being referred to as a 7.4v Lipo, and a 3-cell Lipo being referred to as an 11.1v Lipo. Lipo cells must maintain a voltage between about 3.0 volts and 4.2 volts, and allowing a cell to go much above or below this voltage range can result in damage to the cell. The only way to assure that each cell stays within this voltage range is to charge them individually to a specified voltage (balance charging), or to bring each cell to the same voltage as the other cell(s) in the pack (balancing). A special connector on Lipo battery packs, called a 'balance connector', makes this possible. Some devices simply balance the cell voltages - they do not actually charge the cells. I personally use a Balance Charger that monitors and charges the individual cells of a Lipo. I do not use this charger everytime I charge a Lipo - I sometimes use a simple 'Wall Charger'. And to be honest, I went a long time without ever balancing my Lipos, and never had a problem. However, I do suggest that you consider balancing your Lipos, as they will likely last much longer. You also might consider reading through some RC Forums on this subject to get some other opinions about it.

2. What is a 'C' rating?

The 'C' rating of a Lipo indicates the maximum safe discharge rate. The 'C' refers to battery Capacity measured in milliamp hours (mah). The 'C rating' is a number that is multiplied by the capacity of the battery to give you the discharge rate. (It would be simpler to just indicate the maximum safe discharge rate in amps on the battery pack, but why make it simple?!) The way to determine the maximum discharge rate in AMPS is to take the capacity of the Lipo (mah) and multiply by the 'C rating', then divide the result by 1000. For example, a 1200mah 12C Lipo has a maximum safe discharge rate of  14.4 amps (1200 x 12 = 14400, divided by 1000 = 14.4 amps).

Keep in mind that amp output tells only half the story. You must also know the voltage to determine the total energy output in watts:  Amps x Volts = Watts.  So if your 1200 12C Lipo has 2 cells (7.4 volts), then the total energy output would be 106.56 watts (14.4 amps x 7.4 volts = 106.56 watts). If the Lipo has 3 cells (11.1 volts), then the total energy output would be 159.84 watts (14.4 amps x 11.1 volts = 159.84 watts). More watts will produce more thrust - all things being equal.

If you want to know the true usable energy in a Lipo, you would hook up a meter between the battery and an electrical load (motor/prop) and run from a fully charged state to motor cut-off, measuring the energy used in watt hours (wh).

3. How fast can I charge a Lipo?

Most Lipos are designed to be charged at a 1C maximum rate. This means that the charge rate (milliamps) must not exceed the capacity (mah) of the Lipo. So a 500 mah Lipo should not be charged at a rate greater than 500 milliamps (0.5 amps), and an 1800 mah Lipo should not be charged at a rate greater than 1800 mah (1.8 amps). THIS IS VERY IMPORTANT!!! I have a friend who can tell you why - he nearly burned his house down when a 500 mah Lipo burst into flame while being charged  at a 1000 milliamp rate. BE CERTAIN OF YOUR CHARGE RATE!!! You might consider charging at a lower rate than 1C if you're not in a hurry, as this will help extend the life of your Lipos.

4. When should I charge my Lipos?

Lipo batteries are not fully charged when shipped, so be sure to balance charge them before the first use. Lipo batteries will hold a charge for an extremely long time - years I'm told - so there is no need to charge them right before you fly. I recommend that you allow them to cool for about 20 minutes after flying, and then go ahead and charge them up so they are ready to use for your next flight - whenever that might be. Some chargers will slowly discharge a Lipo battery after charging is completed, so always unhook the Lipo from the charger immediately after charging is finished.