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Canon camera battery chargers: Can a lithium battery be overcharged?


I have google searched this subject and can't find a solid answer, especially from Canon itself. Does it hurt a battery to be left in a charger after it reaches full charge? There are more people of the opinion that it will damage the battery by over charging. I read one article that says no it does not, since all lithium chargers use a maximum charge that is equal to the charge on a battery fully charged, which in effect makes it a maintenance charge. At times I have left my batteries in a Canon wall charger for days at a time. What say you guys???



Li-ion cannot accept overcharge if you don't want to burn down the house.

Boosting the voltage increases capacity, but going beyond specification stresses the battery and compromises safety. Protection circuits built into the pack do not allow exceeding the set voltage.

Keeping a Li-Ion battery at 100% charge stresses the battery and the capacity will decrease faster.

BTW, Canon has this written about keeping the battery in the charger:

"After charging the battery, remove it and disconnect the charger from the power outlet."



When I was a tech (which I'm not anymore), people used to ask me this all the time. I'd tell them - it's fine to leave it overnight, but you want to take it out of the charger as soon as you remember to. The reason why is that our chargers and batteries are "smart," so they check in with each other. If the battery is full, it will report that it's full to the charger, and stop charging, but the periodic check-ins will stress the battery and eventually cause it to not charge as well as it should, thereby damaging the battery. 

Genuine Canon batteries, used with Genuine Canon chargers should never pose a safety risk due to the mechanisms built-in (smart features & auto-shut-off). Counterfeits usually don't have these safety measures (actual knockoffs with our logo on them that we didn't make), some third-party chargers do, some don't. We can't speak to them, because we don't make them & don't test them. 

I hope this helps!  


Stephen explained it perfectly!  Left sitting in a charger, it will keep the battery within a few percent of 100% indefinitely but this is NOT the best way to store a Lithium Ion battery and it will reduce performance and usable life.

So if you forget it once for a couple of days, don't stress out but don't use a plugged in charger as the storage spot for the battery.  And with spring and thunderstorm season getting into swing, in general leaving stuff plugged in for no reason just increases the chance of damage from electrical surge.  I have industrial quality three stage (gas discharge/MOV/HF bypass) surge suppression devices installed at the auto transfer switch for my standby generator and also at the breaker panels for my house, both garages, and barn but I still don't leave sensitive stuff plugged in when it won't be used for a while.


EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video