SlimAgainSoon

I have a small number of batteries that when I put them in my charger (forget the name, but a smart one) it reads "Null," and it won't charge the cells.

Once, I got the charger to wake up and charge the battery, by removing the battery and putting it back in. I've not yet been able to repeat that lucky success.

My understanding is that once a battery drops below a certain voltage, the charger considers the battery faulty, and by design it won't charge a faulty battery.

Any way around this?

The problem stems from batteries left in forgotten flashlights or other devices. Left in there too long, they lose all or most of their charge and the smart charger won't accept them.

ItsJustMe

If you also have a crappy trickle charger, you could plug it in there for 12 hours. If there's any hope of rescue, that will do it. Trickle chargers are too dumb to know any better and they'll try to charge a pickle if you plug one into them.

LordMarv

This sounds like you have a Lacrosse charger? What ItsJustMe said is right, placing the battery in a dumb charger for a couple of hours will bring the battery up to the proper threshold. I'd found a couple of nimh batteries that were what...3 or 4 years old in the drawer. They read null, the crappy charger did the trick.

SlimAgainSoon

...placing the battery in a dumb charger for a couple of hours will bring the battery up to the proper threshold.

Bummer, since I bought the smart charger because my dumb charger died!

David Chen

There are two strategies that have worked for me:

1) If it's not too bad, sometimes just leaving the battery in will work and the charger recognizes it overnight.
2) If it's pretty bad, there's a trick you can do using a paper clip that I haven't had fail yet. It's a variation of the method described here if you search for "paper clip": https://michaelbluejay.com/batteries/charging-tips.html . I actually kept both batteries in the charger and placed a bent clip across just the positive terminals. Note: I have no idea how dangerous this is, and if the battery has been out for too long, it won't retain a charge for very long anyway. They don't seem to like staying discharged for long periods of time.

znomit

I get "High" on my Maha C9000 now and again. Always with old cells that are on the way out.
Charging even briefly on a dumb charger works but the cells get chucked before long.

The MH-C9000 features a high impedance tester which can screen for defective/damaged battery. Most consumer chargers on the market does not have this feature, and therefore will allow charging batteries not may no longer be suitable for use. Maha recommends that batteries triggering a "HIGH" error be disposed for safety reasons, as charging damaged batteries may result in overheating or explosions.However, if you feel the HIGH error is due to a false detection, try charging the battery first in another charger, or drain the battery first using the DISCHARGE mode on the MH-C9000. This is recommended only for advanced users.

SlimAgainSoon

I'll try the overnight trick and see if that takes.

I'll by a dumb charger, if they still make those, if I have to, but would prefer to avoid yet another battery investment.

The paper-clip zap is intriguing. Considering that as a last resort.

dougmc

You can also put one good battery into the charger and your bad battery, and then while both are still in the charger, next to each other, contact the two + ends together. For AA batteries, a razor blade works well for this (you don't have much space), and for AAA batteries a paper clip will work fine.

This is electrically identical to the paper clip "zap", but since you do it in the charger you only have to do it long enough for the charger to see the electricity and take over. (And note that the "zap" even without the charger is very minor if you're charging from a 1.2v battery to another 1.2v battery -- that won't hurt them.)

You only have to do it for a few seconds -- the BC-700 or whatever will see that the "dead" battery now has some voltage and start charging it. Once you see that it's started charging, you can remove your blade.

The problem is that the charger sees no significant voltage from the battery and assumes that there's no battery there. Normally a dead battery still has some voltage in it, but if you leave it discharging for a long time it can go so low that the charger cant' detect it.

Note that you often have to "cycle" the battery a few times to get the charger to fully charge it after this (the "discharge" or "refresh" modes work well for this) and if a single cell is 100% dead from use in a multiple cell device, the odds are it was "reverse charged" (forced to continue discharging by the other batteries even though it was 100% dead already) a bit, which is bad for them and damages them, but usually it's not too bad and most of the capacity of the battery will come back after a few cycles.

wphamilton

Shoot, I'd try the zap first. Momentarily. You're wiring the batteries in parallel, tricking the charger into starting a charge on both batteries. Not too dangerous IMO.

SlimAgainSoon

UPDATE — I tried the zap, using a razor blade I had in the shop to connect the positive ends of two batteries in the charger (charger is a LaCross BC-700, and it was plugged in).

One battery was charging, the other showed "NULL," until I connected the two. Nothing happened, so I held it on for a few seconds and ... works!

The NULL battery showed a voltage and started charging.

This was an AA battery. I did the same later with a dead (NULL) AAA battery, using a wire instead of the razor blade to connect the positive ends. Worked again.

Both of these batteries took a full charge. If they fade quickly under use, I will run a refresh on them and see if that helps.

Thanks for the tip. I've already thrown away some NULL batteries, thinking they were dead and gone.

Glad I asked if this was possible.