How LiPo Battery Packs Are Sized

There are lipo battery sizes ranging from tiny one cell packs for micro flyers to mulit-cell batteries for large scale electric powered planes and heli's. The voltage and capacity of any size battery pack depends on the capacity of each cell and how they are wired together.

To understand how LiPo battery packs are sized, you need to have a basic understanding of voltage and capacity. If you're not that familiar with batteries, that's OK. Just think of voltage as the "muscle" and capacity as the "energy" of a battery. At firs, you should know what is the lipo battey voltage.

LiPo Cells in Series Increases Voltage



To build voltage, cells are added together in series. The voltage (muscle) of the LiPo battery pack will continue to increase as more and more cells are added in series.

Battery packs achieve the desired operating voltage by connecting several cells in series; each cell adds its voltage to the total terminal voltage. Parallel connection attains higher capacity for increased current handling; each cell adds to the ampere/hour (Ah) count.

Some packs may consist of a combination of serial and parallel connections. Laptop batteries commonly have four 3.7V Lipo cells in series to achieve 14.4V and two in parallel to boost the capacity from 2,400mAh to 4,800mAh. Such a configuration is called 4S2P, meaning four cells in series and two in parallel. Insulating foil between the cells prevents the conductive metallic skin from causing an electrical short.

When connecting cells in series, it is the other way around, where tight capacity tolerances (mAH) are HUGELY important, while voltages are not. For instance, a 2200mAH Gens ace 3s lipo can be connected in series with a 1S 2200mAH battery of the same age. the 2S battery is made up of 2 cells in series, and thus the whole system is like a 3S battery. However, again do not use different battery chemistries or capacities in this config. Also if you plan of charging or discharging at high currents, you will need to keep the batteries balanced since there is always a bit of play in the capacities of the cells and one cell will always die or charge faster than the others. In series, that is especially bad if nothing is done about it, it means the battery with the least capacitance will be stressed the most, causing it to become even worse and possibly damage it or destroy it! (it is a positive feedback loop or a chain reaction type effect). Just make sure to keep them balanced.

LiPo Cells in Parallel Increases Capacity

To build capacity, cells are added together in parallel. The capacity (energy) of the LiPo battery pack will continue to increase as more and more cells are added in parallel.

But the voltage (muscle) will NOT increase as cells are added in parallel.

Total Voltage = 3.7 V
Total Capacity =2100mAh + 2100mAh + 2100mAh = 6300mAh

With Gens ace 5000mah packs in parallel you would have one 3000mAh 20c pack. The C rating does not double like mAh in a parallel battery circuit. You can load up the batteries more in this configuration though. Where, individually, the 1500mAh 20C packs have a constant discharge rating of 30 amps, the "new" 3000mAh 20c pack has a constant discharge rating of 60 amps. 

Right Size Pack for Your RC model

Choosing the correct battery pack is as easy as 1-2-3. Most of the current LiPo battery packs of the countless manufacturers sport common dimensions meaning you can easily replace that gnarly NiMH pack with a super-duper LiPo battery. Many model manufacturers offer their own line of hop-up packs to switch from NiMH to LiPo with no problems. Often, when you look closely they offer some sort of 'hop-up' sections where they promote their products on their websites. Just have a look first and see what the model manufacturer has to offer. Most of the time you find optional battery packs very easy and you are also ensured that the pack(s) you buy fit your models chassis just right.

The next tricky part in choosing the correct pack are the overall dimensions of the battery. If the battery you want to replace is of the usual 7.2V Sub-C style than the alternatives are quite clear. You need a pack not longer as 140 mm, not wider as 46 mm and not thicker as 24 mm. These standard dimensions are featured by most battery packs and make swapping easy. If you need special batteries, for example for smaller 1/16 or 1/18 scale models than 85 x 29 x 17 mm are the numbers you need to take care of. But remember: what we tell here is just a rough guide line! Always double check with the actual batteries you use to make sure to order the correct items.

If you look for a battery pack to suit your monster or Short Course truck or even the new generation of 1/8 scale electric off-road buggies the choice is quite easy as these often have rectangular battery compartments. Just measure what the maximum dimensions of the battery compartment are (length/width/height) and have a go on whatever product suits your needs. When it comes to battery packs for the above models many manufacturers offer special solutions for trucks like the Traxxas E-Revo, Mini Revo etc. Again, just have a look around the specific websites and most of the time you will find what suits your needs.