RC LiPo Battery Guide
LiPo batteries are the power source for most RC drones. If you are going to build your first drone, want to achieve longer flight time or have better performance in a FPV race you need to understand the LiPo batteries technology.
LiPo stays for Lithium-Ion Polymer battery. These are rechargeable batteries with three active components:
Cathode – consists of Lithium Metal Oxides
Electrolyte – liquid or gel.
Anode – consists of carbon (graphite)
Like all Li-ion batteries, LiPo’s lose capacity as the number of discharge-charge cycles increases. Without mistreatment a LiPo battery should last between 400 and 1000 cycles. In my next post I will give you some tips how to properly use your LiPo batteries.
LiPo cells have a nominal voltage (V) of 3.7V. That’s the case with your micro quad or smartphone battery. These batteries are marked as 1S. If you are flying a FPV Race drone you probably use 3S, 4S or even 6S LiPo batteries. This means you have 3, 4 or 6 cells connected in series. Connecting the cells in series gives you higher voltage of the battery pack. For example: 3S LiPo battery has a nominal voltage of 3 x 3.7V = 11.1V.
The capacity of the battery is measured in amp-hours (Ah) or milliamp-hours (mAh). Its the amount of electric charge, that the battery can deliver for a certain period of time at a specific C-Rate. A 1300mAh 3S battery can provide a current of 1300mA (1.3A) at a 1C-Rate for one hour. But the same battery can provide a current of 750mA for two hours. In general: the bigger the battery capacity (…and respectively its size and weight), the longer flight time you get. Note: if you choose a too big battery for your drone, it could decrease your flight time because of its weight.
When choosing the right battery for your drone, you should consider its discharge rate or C-Rate. Its a measure of the rate at which the LiPo is discharged relative to its capacity. It allows you to determine the max possible discharge current without damaging the battery cell. One of my Zippy 1300mAh 3S batteries has a 45C-Rate. Lets calculate the maximum discharge current:
1300mAh (1.3Ah) x 45C = 58.5 Amps maximum continuous discharge current
For example: if your quadcopter motors draw 60A in total, you will be fine with that battery.
Generally higher C-Rate is better. The problem is that the RC LiPo manufactures use higher C-Rates for marketing and for most batteries these numbers are far away from real. If you want to know the real C-Rate of a battery, some guys on RCGroups have developed a tool for estimating it using the internal resistance (IR) of the battery.
And speaking of internal resistance, it is extremely important parameter, that affects performance as well as cell life. The internal resistance will increase, due to accumulation of oxidation products at SEI layer on the anode, as the number of discharge-charge cycle rise. If you want to measure the IR of your battery, you either need a special IR Meter or a battery charger with that function. The latest version of the Wayne Giles ESR Meter give you also the real C-Rate of your battery. Note: you should measure the IR at about 20° Celsius, because IR varies with temperature. The lower the IR, the better the battery is.
I hope my article is easy to understand and now your know a bit more about RC LiPo batteries. If you have any kind of questions or recommendations, please leave me a comment.