We discussed how to dispose LiPo batteries, but we still haven’t touched on when we should throw them out. So in this article I are going to talk about how I determine if a LiPo battery should be thrown away.
The Average Lifespan of a LiPo Battery – Discharge Cycles
If you are lucky enough not to break your LiPo battery before its end of days, it should have an average lifespan of about 400–500 cycles. One cycle means a battery being fully charged and then discharged.
Of course this also depends largely on factors like how much “abuse” you put your batteries through, and how you handle them on a daily basis.
500 cycles might sound a lot, but for us flying mini quad, it’s extremely likely that we damage them way before we hit that number
One useful battery health indicator would be internal resistance (IR). As explained in my LiPo battery guide, IR determines how effectively the battery can deliver the current to your quadcopter. High IR means lower performance, and more heat generated during charging and discharging.
Each cell in the LiPo battery has its own IR value.
New batteries should have a relatively low IR, and it increases during the use of the battery. IR can rise more rapidly when:
- Over-discharging (e.g. below 3V per cell) and overcharging (e.g. above 4.2V per cell for non-HVLi)
- Pushing the battery too hard by discharging at a current higher than it’s rated for an extended period of time
A visual examination of your LiPo battery can help you determine if it should be replaced.
LiPo batteries used on drones can become deformed in a crash since they are exposed on the outside of the frame. Some people take the risk carry on using these dented batteries without much of a problem. But the risk of fire increases so I’d personally just dispose them.
Your batteries can also become “puffed” after some abusive uses or they are just simply getting too old. Perhaps it’s not as bad as the one in the picture below, but you might notice it’s getting fatter than it was, this is a sign of puffed/swollen LiPo.
Unbalanced Cell Voltages
It’s pretty normal that the cell voltages are slightly different after a flight, maybe one is at 3.55V, one is at 3.59V, and another at 3.61V… The point is, they should all be within reasonable range.
You should be cautious when the gaps grow. When the internal resistance of particular cells are higher than others, they discharge slower and therefore have a higher voltage remained at the end of the flight. Eventually this might lead to over-discharging of other cells in the battery and cause swelling.
This is also why you should always “balance charge” your batteries in case of over-charge.
Check Temperature While Charging
If your battery gets warm during charging, then it’s a very, very important sign that your battery might have a problem. LiPo batteries shouldn’t get noticeably warm when charging at reasonable rate i.e. 1C or even 2C.