We discussed how to dispose LiPo batteries, but we still haven’t touched on when we should retire them. So in this article I are going to talk about how I determine if a LiPo battery is old enough to 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 is when you fully charge and then discharge the battery.
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 :)
LiPo batteries don’t have an expiry date printed on them. But from my personal experience, I did find new batteries perform better than old batteries, even when they just sit there and not being used much.
I generally find batteries that are 12- to 18-month old have noticeable drop in performance, and I would probably replace them after two to three years even when they might look fine on the outside. That’s just me, other people might have different opinions.
It’s helpful to label and date your battery packs when you first get them in from shop.
Battery Health – Internal Resistance
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 maximum discharge current and more heat during discharging.
New batteries should have a relatively low IR, and it increases during the use of the battery. IR can rise more quickly 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
IR can be measured with most LiPo chargers these days (for example the iSDT Q6). You get shown the data every time you charge it.
I recommend writing down IR when you first acquire your batteries. You can then compare the figures to determine how your batteries are doing, and if the number has increased considerably, the pack should be replaced. Make sure you use the same equipment to measure IR because different devices can give very different IR measurement.
A visual examination of your battery can help you determine if it should be replaced.
Your batteries can become deformed in a crash. I’ve seen people carry on using these batteries without much of a problem. But the risk of fire increases so I’d personally just dispose them.
Further Reading: Here are some tips to protect your LiPo batteries from physical damage
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.
Pay Attention to Performance
Battery performance goes down hill when they get older, symptoms like
- Not holding it’s max voltage after charge
- Voltage sag is noticeably worse
- Holding less mAh capacity, your run time has noticeably declined
If you noticed any of these problems, then you should consider replacing the battery, unless you don’t mind the decreasing performance.
Another thing to keep in mind is the temperature of the LiPo after a flight. If a battery is getting way hotter (can’t hold it in your hand for more than 10 seconds) than others, it’s also a sign of getting old.