Am I correct in thinking that a nickel metal hydride battery cannot be tested using a standard battery charger, because the voltage is 1.2 volts instead of 1.5 volts? Also, if the battery charges in about five minutes (after a discharge) can I assume it is defective anyway?
No, in reality, it depends on the charge state. You can get devices that are happy to stick higher currents on a cell for a few seconds and tell the approx charge or health of a cell of any voltage. NiCads used to be 1.2v too, remember. I think that many devices do not charge the batteries correctly. Things like door intercom units, and walk about phones tend to charge the cells in series and this means that the first battery that goes down often gets reverse charged by the current through the phone, making it get even worse until you find you might have a couple of good cells and some duff ones ready for the bin. I have a Roberts radio here, and it charged the batteries as separate cells, and these last a lot longer than in one that charges them in series. Of course you do get dodgy cells, but from your message, it is very true that if one does measure very very low volts it will eventually not fully charge either, and this can be seen when you get the effect that no mater how much you charge them they are not lasting very long. Your five minutes is a very typical end point I find, for whatever reason they suddenly act like there have an internal resistor both in series and also draining the cell while its lying around.
While on the subject of batteries, does anyone know what they are doing with these new Energiser cells that are lithium single cycle primary cells that according to the literature will run a video doorbell for 2 years, against a couple of months for Duracell's. Is this really the truth? Brian
What's a 'standard battery charger'? Any kind of AA/AAA/etc charger will be designed for 1.2v NiMHs (or, if it's old, NiCds). Do you mean a 'standard battery tester'? In which case it depends on the tester (there might be 'standard batteries' but not 'standard testers').
If you put the battery on a smart charger and it reckons it's charged in 5 mins then it does point to it being very low capacity - there's not much energy going into it in that time.
Theo
To check AA and AAA NiMH rechargeables I use a Technoline BL700 unit, the previous version to this:
This can do the following to 1 to 4 cells, individual bays can be independently set:
Charge
Discharge and charge
Test (charge, discharge (measuring mAh), recharge)
Refresh (at least 3 cycles of Test, displaying maximum mAh obtained, stopping when there’s no improvement).
It’s interesting to take a ‘dead’ cell, such that the unit won’t even recognise, leave it in place for an hour and the cell then comes alive and starts charging. At this point I reset the mode to Refresh, and watch the mAh build up as the cycles progress.
I guess I’ve recovered enough ‘dead’ cells back to useful life to more than pay for the charger (£30 when I got mine).
Yes, my mistake. It is a multimeter with a battery test facility.
Thanks. This is what has happened. I think I'll put them all into the recycling. When I tested using the meter, half of them show as bad already, but I wondered if this could be because they are 1.2 instead of 1.5V.
Thanks. Mine is an old Ansmann and far less sophisticated.
So what kind of battery is it designed to test? It must say (in the accompanying documentation) as there are loads of different voltages/technologies of battery. Presumably it just registers the voltage with or without some kind of load.
(Reminds me of the devices that suppliers of car batteries have; they connect it, press a button and tell you that you need a new one (££££). I doubt that they can tell whether the battery is knackered or just is discharged due to a faulty charging circuit in the car.)
So does it say "good" or "bad" or does it show the voltage?
I've got lots of old NiMH batteries that I use in things that don't use much power, like a novelty "mood cube" that changes colour.
Found it - external 1.5V dry cell battery checked with a 15 Ohm load. Needle swings to a green good zone or a red bad zone.
I just wondered if it would work with 1.2V batteries also.
Or remember they used to attach testers to the outside of Duracell batteries?
Well, it will, but obviously it's unlikely to reach the green zone even if fully charged !
Anyway, don't you use your tongue ?
15 ohms is quite a low resistance. Clearly if it is expecting 1.5V it won't like 1.2V even if there is very little drop. By "dry" batteries do they mean zinc carbon, zinc chloride or alkaline? Do they mean AAA, AA, C or D size? Sounds like quite a crude tester.
Check the voltage when it is connected to whatever it's supposed to power, or with a resistor which draws similar current. There should be very little drop in the case of NiMH.
I have the same charger - been very happy with it. Evey now and then I put a battery in that's come from a 2/3/4 cell device and it reads Nul. Not tried leaving it for a length of time, I just bang it into a cheap "fast charger" for 5 minutes or so then run the whole set through the Refresh cycle (assuming I've got the time, it does take a while).
Not sure if I'm doing the right thing but it appears to work.
those don't tell you much, just terminal voltage under a small load.
if the meter expects 1.5v it's not going to tell you anything useful unless you ignore the good/bad & interpret the voltage yourself. Cycle the cells a few times, charging them 1 at a time, you may find they then work.
it should tell you terminal voltage but the good/bad will be completely wrong,
his symptoms fit as-new batteries. Only took 5m charge then read 1.2v, misinterpreted as dead.
That’s more or less what I do. I found by accident that the BL700 would bring a dead (the dreaded ‘Null’ reading) cell back to life - I’d just inserted a cell when I was called away, and came back an hour later to find the cell happily charging. Since then I’ve recovered several such cells, that have gone on to give good service where otherwise they would have been thrown away.
I’ve lost the instructions for the unit, but I vaguely recall them saying it won’t recover dead cells, but perhaps that was just a very cautious statement to cover themselves.
Only if they have had a one time deep discharge or reverse charge do they seem to recover and of course you don't know if this is the case as us punters are never told how a device like a phone cradle is doing the charging. Brian
Or perhaps it was already near fully charged? Easy to check using the multimeter on a (dc) voltage setting.
It sounds as though the battery tester is expecting to see a 1.5v cell. If so a fully charged NiCad or NiMH might not make it up into the "green/good" section of the display.
Thanks. Change of plan. I have put all the cells back in the box. I think I'll get a new tester.
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