All about Lithium Polymer Batteries

Here you will find some collective and useful information about lipo batteries and their care.

---What charge rate should I use?--

Lipos require a special type of charger that uses the CC/CV method (Constant Current/ Constant Voltage). Provided your charger is capable, you will be best served using a 1C charge meaning you charge the pack at 1x its capacity. A 2200mah pack will be charged at 2.2 amps, an 3000mah pack at 3 amps, and a 1800mah pack at 1.8 amps and so on. Some companies suggest that their lipos can be charged at 2C or even some at 5C, it’s always best to use caution with charge rates like these. A 2200mah pack at a 2C charge rate would be 4.4 amps, a 5C on the same pack would be 11 amps. Charge rates like this can be convenient if you’re waiting to get back in the air, but in the end using a 1C charge or (or even less) will help your battery cells last longer. To figure your charge rate you simply take [capacity] x [charge C rating] % 1,000; so you have a 2,200x4(charge C rate, not pack C output) = 8,000 % 1,000 = 8.8 amps.

--Lipo Balancing--

Lipo packs made up of more than one cell in series will require balancing. Lipo cells, no matter how good, will sometimes vary in terms of their exact capacity and discharge rates in relation to the other cell(s) in their pack, so it is important that any imbalance between cells is equalized during or after charging to prevent possible damage due to over discharging or over charging even. Whereas a normal charger will pump current into the pack as a whole, only stopping when the target voltage is achieved, a balancer (or balance charger) will read the individual cell voltages and bleed off excess voltage/current from any cell that is getting ahead of its companions. The amount of current a balancer can drain varies, but around 300-500mah is fairly typical, meaning that small imbalances can be fixed during a charge, but larger imbalances may require longer to correct before all the cells are at an equal level of voltage & the charge can be terminated. The fully charged voltage of a lipo cell is 4.2v, so any higher than that and damage may occur; any lower than about 3.0v-3.2v and damage will also occur; 3.2-3.5v is seen as the ideal minimum voltage before a lipo cell should be stopped from discharging. Storing lipos for long periods without use or cycling (discharge and charge) them may result in the cells becoming partially drained and out of balance, so checking them occasionally is recommended. It is also HIGHLY recommended that lipo batteries are stored at 3.8v per-cell (50% capacity) if you’re not planning to use that pack within 5-7 days. Most quality charges have a storage charge mode on them, if your charger does not then run your pack down then watch the charger until you reach 3.8v per-cell.

--C rating and what it means—

The C rating essentially determines the maximum output of the battery, the higher the C rating the more amperage or “power” your battery is capable of putting out, the lower the C rating the lower the output. Now with this said we need to note that a higher C rating equals a heavier pack, a 2200mah 3S 25C pack vs. a 40C (or above) pack of the same specifications will typically result in the additional weight of 28g (1 ounce) or more in the 40C counterpart. The effects of the weight difference will depend on your quad and what you’re trying to achieve in your flights, but for general flight you will likely notice less run time on the higher C rated pack because the additional weight requires the motors to work harder – and in return when you’re nearing the end of the pack your quad will begin to get very lazy and lethargic.

Higher C rating batteries can be useful in some applications that cause an extremely high draw in amperage, and in terms of aircraft this would mean acrobatics. Some pilots who fly 3D CP helis prefer to use higher C rating packs as this will allow them to return from stalls or flips and extreme maneuvers, the higher C rating can provide that extra burst of amperage to the motors allowing them to reach maximum RPM more quickly. In racing quads the extra amperage can be useful as well when attempting barrel rolls and flips, or just that extra acceleration to get ahead of your fellow racers. Keep in mind a higher C rating pack will NOT make your quad faster as this is a common myth upon some message boards, the higher C rating will allow the motors to draw more amperage if it is called for. Another common myth is that batteries push amperage and this couldn’t be more false, instead the amperage is drawn from the battery from the electrical system. When using a higher C rating battery in a racing quad it is always wise to use a lower capacity battery pack to compensate for the weight difference. For instance if you’re normally flying on a 2200mah 25C pack you may want to try a 1800mah 60C pack. There are some high-output 1800mah 3S packs that weigh around 170 grams which is about the same weight as a stock Runner 250 2200mah 25C pack. It’s all very relative to your application when it comes to choosing a higher C rating pack and chances are if you’re an experienced acrobatic pilot you wont need a suggestion of what to use.

For terms of standard flying I always recommend using a pack of similar size and weight to stock, if the quad was designed on using one style and weight of packs it’s best to stick with that unless you know what effect you’re after otherwise. Large C rating packs are not typically seen in large aerial photography style drones as it’s not typically necessary and would likely just cause unwanted weight to your payload.

In order to figure out our lipos maximum discharge in amps we need to use what we learned above in charge rate. Take a 2200mah 25c pack, it will be 2200 x 25 % 1,000, so it will look like 2200 x 25 = 55,000 % 1,000 = 55, our pack is rated for an output of 55 amps according to the manufacture specifications. The formula remains the same no matter what the C rating and mah rating are.