Note: All of this applies to lithium-ion batteries in general and not just cordless drills.
We develop battery myths. Generally these myths are based in truth and following them would be good, but we’re making different kinds of batteries with different characteristics now.
I wrote this post because I see many people whose li-ion batteries have died much sooner than they should and I think we haven’t spread the word on how to care for li-ion tools. So let me set the record straight.
Lithium-ion batteries do not have “memory”
NiCad batteries can exhibit a “memory” effect, where consistently draining the battery to a certain point will cause the battery perform poorly past that point in the future. So you want to completely drain a NiCad battery regularly. But lithium-ion batteries do not have this problem. In fact they have an opposite quality.
Completely draining a li-ion battery may damage it
That’s right. Instead of trying to drain a li-ion battery you should try to charge it before it’s completely drained, the opposite of what you should do for a NiCad battery.
But I don’t want you to develop a complex where you’re scared to use your drill for more than 5 minutes. Li-ion batteries have circuitry to prevent them from completely draining. So you can safely use your drill to close to exhaustion. But
Never store your drill when it’s almost dead
Lithium-ion batteries have low self-discharge (the amount the battery drains when not in use). But they still have some self-discharge. And if you put your li-ion battery on the shelf almost dead and leave it there for 3 months, it’s likely to drain enough to cause damage.
The ideal charge state for long-term storage is around half capacity. Leaving the battery in a completely charged state for long periods will slightly but permanently lower the capacity. But since there is some self-discharge, if you put it away full after a month it won’t be full anymore. Another minor point is that li-ion batteries are best store cool, but not freezing.
The takeaway here is it’s a bad idea to leave the battery charging all the time. And it’s a bad idea to store the battery empty or almost empty.
Extreme temperatures degrade performance
If you want your battery to last to its full potential, then you should avoid temperatures, above 120 F and below freezing. So you shouldn’t leave drill battery out in the truck in the summer or the winter. If you want to store your spare battery for long periods, take it to half charge and put it in the refrigerator. It will be safe for years in there.
Help spread the word
If you know people with lithium-ion tools point them to this article. Share it on Facebook or Twitter or blog about it if you’re into that. Friends don’t let friends abuse their li-ion tools.
I just bought a cordless drill with a lithium ion battery, and was not aware of things that can damage the drill or battery. Very informative article.