Shop Talk

Danger of Overcharging Power Tool Batteries

  • Leaving a power tool battery on a charger for too long, or even all night long, is one of those simple mistakes any craftsman can make – you plop your battery down to charge, you eat your dinner, you watch Jeopardy or the news, and suddenly you have completely forgotten about that battery charging in the garage or behind the sofa. It happens. Few of us, though, truly realize how just how detrimental this can be to your battery.

    Overcharging generates an excess amount of heat within the battery and charger that can and will deplete the overall life and general performance of your generally very expensive batteries. Every second your battery is unnecessarily connected to a charging terminal, you are losing valuable time with your battery – the thing will die prematurely and you’ll be stuck with the bill for a new one, and likely a tear or two in your eye. Its never easy to lose a battery.

    Most chargers will indicate when a battery has received a complete charge, and what’s more, most chargers will tell you exactly how long it will take to recoup your battery (i.e. “this is a 15 minute charger” or “this is a 30 minute charger”). This, however, is sometimes not enough for the busy or forgetful craftsman, and although these days many chargers have an integrated interior cooling fan, some have a chime to notify when a battery is completely charged, and others still will stop delivering charge to your batteries, none of them will automatically shut off. This means your battery and charger are still hot, and your battery is still connected to the charging terminals. This should mean at least several things to you: firstly, that you are depleting the life of your battery with every overcharge, secondly, that you are wasting energy, and thirdly, that you are at a much greater risk of electrical fire. Keeping your battery on a charger for too long is not only dangerous for your batteries, but also to yourself and your environment as the heat generated and the electrical nature of battery charging is always a fire hazard. Ultimately, overcharging is bad for everyone. I suggest err on the side of undercharging (unless, of course, you are still using an old NiCad battery which will usually experience “the memory effect”, but that’s an entirely other story). Undercharging may be frustrating once or twice for just a minute or two, but will ultimately save you and your battery from a lot of avoidable heartache.

    Despite all this, it is still easy to forget your charging batteries; its easy to leave them charging for seeming endless hours, but you must stop. Stop or suffer eternally the under-performance of overcharged batteries. Tie a string ’round your finger, set your alarm clock, write a note on your hand, but remember to pull those batteries off your chargers. You’ll be glad you did, and your batteries will perform optimally for a longer, healthier time frame.