I have learned how to bring some of those power tool batteries back to life. Do not throw them out just yet.
When we are told that these batteries are rechargeable sometimes we assume they always will be. If your anything like me, you find out that they are sometimes not. I noticed some friends that use theirs a lot, do not have the issues I have with keeping them recharged. I believe I have stumbled on the reason. I will explain to you how to bring some of them back to life. When you do get them back, use them more often. The longer they sit around, the harder they are to bring back.
First … How does the battery charger itself read? How does it know if there is a battery even connected? If I just put anything in the charger will it attempt to charge it. No, it does not. It knows when a battery is plugged in because it reads a voltage connection between the two terminals. If you were to copy the size of a battery out of wood, weight, size, even the tabs that connect positive and negative, the battery charger will not turn on.
Second … The battery charger only turns on when it knows there is voltage but not enough.
How does it know to turn off? Because it has a built in voltage regulator that shuts off when the item plugged in (battery) has the correct amount of voltage.
Battery with Correct Amount of Voltage
Third … How does this have anything to do with my battery? When your battery is dead, the charger does not know it is plugged in. There is no voltage or enough voltage for it to read the battery. So it will tell you the battery is defective by lighting up the defective light.
Fourth … Can we trick the charger into thinking the battery is good and just turn on the charger? Yes, there is a way. We need to excite the battery. Just as if we wanted to excite a coil or an alternator on a car. We need to apply a small amount of voltage to the battery. There are a couple of ways to do this.
Fifth … Unplug the battery charger cord and plug it back in multiple times quickly. The battery charger will read the battery voltage by applying a small amount of voltage to the battery to see if it gets a response from the battery. this could take several attempts, but believe me, it works.
Unplug Battery Charger
Sixth … Another way to excite the battery is to use a different battery charger, and touch the terminals on your battery (positive to positive and negative to negative) a few times. This should be done quickly to just excite the battery. Do not hold the connections to the battery, just simple small touches, then put the battery into the charging station.
Seventh … The most important part of your process, do not remove the battery until it is fully charged. After it is fully charged, do not replace it half charged in the charger. Use the battery completely until it is dead, then recharge it completely one more time. this will ensure you get the full capacity of the battery. If not, you will experience a battery that only works for a short time.
Here is a video showing this process.