My cheap 2-hour walmart charger can only work if 2 or 4 batteries are inside it. If I put just one in, it won't work. Can I charge a dead one with a fully charged one? Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

Buy a decent charger and stop frying your batteries.

What is a decent charger you recommend?

Nimh or nicad ?

It's tricky, I'm not in the same country as you.

However some cheap chargers trickle charge 4 batteries in parallel but independently - because they trickle charge you can estimate charge time based on capacity and overcharging isn't an issue because the current is so low.

I use a computerised charger.

I strongly suspect that your 2 hour charger just outputs high current for 2 hours and then stops - not very good for a partly discharged or lower capacity battery.

Hope this helps....

I have a LaCrosse and it's worked fine for me. It came with a nice set of batteries to get started with.

https://www.lacrossetechnology.com/900/index.php

This is my charger ( nimh ):

https://i.walmartimages.com/i/p/00/02...59_500X500.jpg

I think it has some intelligence not to overcharge since it automatically turns off when batteries are charged.

That's a 1 hour charger ?

I couldnt find my exact model, but that is quite close to mine.

See

Battery Charger Comparison

From the chargers listed there, I have TurboCharger 4000 and am very pleased. It has a thermal switch that terminates the charging if the batteries begin to heat up. There are other smart charger options there, including the possibility to charge an odd number of cells. Simple chargers either take forever to charge or fry the batteries. I would not charge a set where one battery is dead - either the other will not charge or you will have a good chance to damage the other as well.

If you are lucky the charger is cutting off before the battery has reached full capacity as it isn't possible to properly charge a NIMH that quickly.

In any case the number of charges you get from the batteries will be a lot less than careful charging and the capacity will drop a lot quicker too.

It's a trade off - you get the convenience of a fast charge - the batteries pay the price.

Higher capacity batteries are not suitable for fast charging.

generally any charger will work in this situation.

you don't need a fancy charger, despite what others may claim.

better off buying a cheap multimeter so that you can make this determination yourself.

typically they'll all (2 or 4 cells) charge to within 0.1v of endpoint

Oh really ?

Just how does a 2 hour charger detect the negative delta V of each battery when it has a minimum of two batteries attached to it ?

And isn't capable of charging individual batteries ?

Sigh....

0.1V of what endpoint?? The consumer is supposed to take measurements with a meter, produce a chart and decide that the voltage has already gone through the peak, very weakly pronounced in the case of NiMH. I would appreciate if you could record your actions and post them on YouTube or elsewhere so all of us stupid getting smart chargers could learn.

+1 if you are using a cheap charger you are either going to over or undercharge every battery you put in it - what are you suggesting, checking the battery with a multimeter every 10 seconds in a vain hope of detecting a minute voltage drop ??

I think the OP is hoping for good advice.

Would just like to say that I don't like FAST chargers.

A big problem with the 1/2hour chargers is that the battery gets very warm, and the heat drastically shortens its lifetime re charging cycles, but does, in my experience seem to effect the length of each actual charge as well.

I find 6-8 (12 if necessary) hours depending on capacity adequate.

Lets face it, if you need a battery NOW, it would make little difference if it was an hour away or 12 hours away, you still wouldn't have it NOW.

A billion people recharge batteries successfully every day, simply by following the instructions - all without the sage wisdom expressed in this thread.

The OP asked for advice - take it up with him.

Oops, I thought you were the source for the wisdom.

But how many actually realise the full life time form their batteries?

I can tell you that before I became wise to the pitfalls of cheap and/or fast chargers, I was having under 1 year old and under 100 charge cycle batteries going flat far too quickly or just not holding a charge at all, constantly.

1 decent charger later and I have not had a single battery to date that has not met its expectations.

I am a big fan of the new hybrid batteries too.


Anyway, advice was asked for, and has been given.

Whether it is good advice or not, that is for the OP to decide.

And while we are talking of sage wisdom:

Ha ha ha ha ha ha ha ha !!!!

Thanks for all the replies, I take it the answer to my question below is no.

Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

Your cheapo wal-mart charger... - Probably not.

There are chargers that will charge individual batteries - and even tell you if a cell is dead.

You pays ya money and takes ya choice.

I'll try to answer accurately: No, I dont believe it is possible.

Note: that refers to intelligent chargers

There are several ways a charger can detect when a battery is fully charged and a decent charger will often use several at the same time.

If your charger has a temperature monitor it might cut off before the healthy battery is too badly damaged.

If your charger detects the delta peak (very unlikely when charging 2 batteries in parallel) I would say you have no chance of not damaging the healthy battery.

Sorry, a cheap charger is a cheap charger.

A charger that charges cells in pairs, takes the pair connected in series. A smart charger will usually figure out that something is wrong and refuse to charge or will switch to a trickle mode. It has no means of disconnecting those cells from each other. The dumbest fast chargers have only a time cut-off and will try to proceed with an unclear outcome.