Last week, we discussed the basics of LiPo batteries in this post. Now, let’s get into what the numbers mean and how to choose a battery that’s right for your helicopter.
All Lithium Polymer cells have a nominal voltage of 3.7v per cell, and when fully charged the cell should read 4.2v. Another important voltage to remember is that, when discharged, each cell should never fall below 3v. If a cell should fall below 3v, then it can sustain irreversible damage. But the real question is, how much of the battery capacity can I safely use without hurting it, and to get the most life out of the battery. The quick answer is to always keep the battery voltage between 4.2v and 3.7v. But this leaves a gray area between 3.7v and 3v, and to examine this area we have to be concerned with battery life cycles. If the battery is never discharged below 3.7v you can expect to get between 100 and 150 cycles out of the battery. This is where a cycle is defined as a charge and discharge. But should the battery be discharged below 3.7v, but not down to 3v, the number of cycles of the battery will be reduced. As an example, suppose you fly until the battery is discharged down to 3.4v. That may reduce the useful cycles to something below 100, let’s say down to 75. There’s no way to really tell how much damage is done to the battery, other than to say it has been hurt and will not give the normal amount of cycles it was originally capable of producing. Note also during this discussion I am referring to individual cell voltage, so you must multiply these numbers by the total number of cells to get the overall battery voltage.
S – Number of Cells – LiPoly RC packs are made up of layers of multiple cells. If the battery’s rating is 3S this means it has 3 layers of 3.7v each, for a total rated voltage of 11.1v. In other words, it’s a 3 cell pack.
For a battery to be right for your model it must fit within the models battery compartment and also balance the plane correctly. It’s temping to choose the biggest and most powerful battery your model can handle, but this will sacrifice flight performance, and if the voltage is too high it will destroy the ESC or motor. Check the ESC and motor specifications to ensure you have the right pack and then check the models CG (Center of Gravity) to decide on the right battery weight.