There are many different kinds of battery, many of which have specifications such as capacity, S configuration, P configuration, C rating etc. How do I translate these into knowing what is best for my multicopter?
When looking for a battery, there are a number of factors to consider: the voltage (or S rating), the capacity, the C rating, the type of connector, and the weight:
You will often see batteries having an ‘S’ rating on them, for example 6S or 4S. This is the number of cells, which directly impacts the voltage output of the battery. Just to be clear, I am specifically talking about LiPo batteries here as nominal voltages vary between battery chemistries.
Each cell will add a maximum voltage of 4.2V, and a nominal voltage of 3.7V to the battery, so to figure out the nominal voltage of a battery, just multiply the number of cells by 3.7, so a 3S battery has a nominal voltage of 11.1V and a maximum voltage of 12.6V. This is very important using a battery with too low an S rating will likely make the aircraft more sluggish, but using a battery with too many cells is likely to make the aircraft more on fire.
You may see batteries written in the format 4S1P or similar. This means that there are 4 cells in series that are treated as one parallel cell - i.e that there are no other parallel cells.
The capacity of a battery is measured in mAh, or milli Amp-hours. This is the number of milliamperes the battery can output at the nominal voltage if the battery is discharged over the course of one hour. For example, a 1300mAh 4S battery could output 1.3A at 14.8V for one hour.
In general, a greater capacity will mean more flight time, however there are caveats, an important one being the battery’s weight (which I will talk about later).
The C rating is the maximum discharge rating, and it acts as a multiplier of the capacity. For example, if I have a 1300mAh LiPo with a C rating of 100, the maximum current output will theoretically be 100*1.3=130A. Obviously, a higher theoretical discharge rate should give greater performance.
These metrics are very variable between brands, however. What Turnigy considers to be 100C may only be 75C for another brand, so there is in reality very little point comparing C ratings between brands.
C is also used when charging. You may have heard people say ‘charge at 1C’ or something similar, and this means the same thing. For example, charging a 1300mAh LiPo at 1C would be charging at 1.3A.
The way you get the power from your quad is also very important. There are many connectors currently in use, but here is a rundown of the most common used on a multicopter:
- JST PH2.0: small white connectors most often used on Tiny Whoops, sometimes used in series on a toothpick.
- BT2.0: small white connectors most often used on Tiny Whoops, sometimes used in series on a toothpick.
- XT30: small yellow connectors, most often used on toothpicks and 2/3 inch quads.
- XT60: medium-sized yellow connectors, pretty much the standard for 4-7 inch quads.
- XT90: large yellow connectors, often used in parallel or series on larger Beast Class or X Class builds
- Deans: not commonly used in multicopters, however many batteries you will see do have this style of connector, which often has burgundy plastic.
As mentioned before, more capacity usually brings more weight, which introduces the problem of balancing capacity and weight.
For example, a toothpick with a 5000mAh should be able to fly for an hour, but would in reality be unlikely to last a minute if it could even take off due to the large weight of the battery. Some people say that your battery should not make up more than a third of the weight of your drone, however, you can huddle this based on your motors’ thrust and your build’s weight.
There are many factors when choosing what battery to use for your drone, however, all of the above aspects are vital in ensuring good performance and longevity of your aircraft.