I need to recharge a pair of AAA Ni-Cd batteries every few days. I don’t want to charge them for longer than the suggested charging period. I’m using an old charger; I suspect that it does not have any internal cut-off circuitry.
Now, I have one of those 24-hr timers you use to turn your house lights on/off when you go away for vacation. So, I can hook up the charger to the timer, and it will kill the charger – essentially unplugging it – at the end of the charging period.
But the newly charged batteries will still be connected to the charging terminals. That got me wondering: Will the charger begin to drain the batteries once the power to the charger is killed?
If the charger is that old and has no internal cutoff (probably a trickle charger), I suspect that it is nothing more than a transformer, rectifier, and current limiting resistor, which won’t drain the battery if it is left connected while unpowered (as **beowulff **said, check first).
I’ve never seen a charger with this facility. I suppose you could easily use one of those wall timers people use to make the lights come on when they’re not at home.
My charger has a switch you can use if you want to discharge the batteries, which suggests that they won’t normally discharge.
That’s exactly what the OP wants to use, hence his question about whether the batteries will discharge through the disconnected charger. However, if the charger is as I suspect (always check first, but a charger that’s so old and simple that it has no internal timer is probably one that just has a diode on the output, which will naturally prevent discharge, plus a resistor to limit current; also probably a trickle charger, where overcharging only shortens the life, regular/fast chargers must have a cutoff or bad things, including explosions, can happen), it probably doesn’t matter either way.