# If you regharge Ni-Cd batteries, unplug the charger w/ batteries still attached, will they drain? **URL:** \ **Category:** Factual Questions\ **Created:** [January 2, 2013, 9:07pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880 "2013-01-02T21:07:51Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![stuyguy](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@stuyguy](https://boards.straightdope.com/u/stuyguy)\ **Post date:** [January 2, 2013, 9:07pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/1 "2013-01-02T21:07:51Z")
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? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 2, 2013, 9:11pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/2 "2013-01-02T21:11:46Z")
The only way to know is to use a mA meter to test it and see. The charger may have an internal diode, but it may not. ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [January 2, 2013, 9:45pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/3 "2013-01-02T21:45:42Z")
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). ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [January 3, 2013, 4:24am UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/4 "2013-01-03T04:24:06Z")
Can you set the timer to start charging late instead of stopping early? ---
**Author:** ![stuyguy](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@stuyguy](https://boards.straightdope.com/u/stuyguy)\ **Post date:** [January 3, 2013, 5:29am UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/5 "2013-01-03T05:29:17Z")
> [@AaronX](#): > > Can you set the timer to start charging late instead of stopping early? Huh? I don’t understand this question. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [January 3, 2013, 6:57am UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/6 "2013-01-03T06:57:58Z")
I mean, rather than stopping it after 2 hours, can you set the timer to start charging 2 hours before you need the batteries? ---
**Author:** ![PaulParkhead](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@PaulParkhead](https://boards.straightdope.com/u/PaulParkhead)\ **Post date:** [January 3, 2013, 4:58pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/7 "2013-01-03T16:58:50Z")
> [@AaronX](#): > > I mean, rather than stopping it after 2 hours, can you set the timer to start charging 2 hours before you need the batteries? 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. ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [January 3, 2013, 5:37pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/8 "2013-01-03T17:37:14Z")
> [@PaulParkhead](#): > > 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. 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. ---
**Author:** ![PaulParkhead](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@PaulParkhead](https://boards.straightdope.com/u/PaulParkhead)\ **Post date:** [January 3, 2013, 10:11pm UTC](https://boards.straightdope.com/t/if-you-regharge-ni-cd-batteries-unplug-the-charger-w-batteries-still-attached-will-they-drain/645880/9 "2013-01-03T22:11:24Z")
> [@Michael63129](#): > > 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. Damn, I don’t normally misread the OP _that_ badly.