AA rechargeable battery types

[wombat88]

I have a Cobra hand held radio that is around 18/19 years old. It works perfectly well.

However...
I decided to replace the batteries recently. It takes 6 x AA. I threw away the old ones in the convenient battery recyling point in the local supermarket. Dammitt!

I bought Energiser 2300 mAh NiMH batteries.

The battery charging stand that came with the radio does not work with these batteries. means I have to open up the radio and remove the batteries to charge them.

I'm guessing that if I could get some rechargeable batteries of a type that would have been around 18/19 years ago the original charging stand will work.

So what type of battery am I looking for?

 

[pvb]

So what type of battery am I looking for?

It would most likely have been supplied with NiCD rechargeables, you can still buy these.

 

[Paulg25]

Did they make NiCD in AA format?


Edit..
Just googled. They did.
Still available.

 

[davidej]

I would expect any charger designed for NiCads to work perfectly well for NiMHs as well.

 

[Paulg25]

I would expect any charger designed for NiCads to work perfectly well for NiMHs as well.

Just looking that up and came to the same conclusion.

 

[Paulg25]

The battery charging stand that came with the radio does not work with these batteries.

Genuine question. How do you know it doesn't work? Not showing a charge light? Batteries still flat after leaving on charge overnight?

 

[Refueler]

Yes .. NiCd was the standard years ago in all the common battery sizes ... AA ... AAA ... C ... D etc .. and then the 'Greenies' objected to the cadmium which was ending up in Landfills ..... NiCd was generally withdrawn from the shelves for that reason. You can still buy - but usually for specialist applications.

NiMh was already around - but wasn't as capable of the high amp rates NiCd's could do.

One of the limiting factors of NiCd's was capacity. This is why today you see NiMh with incredible capacity for same AA ... AAA .... sizes etc. BUT that comes at a penalty.

As Capacity is increased in NiMh - the output capability in amps reduces .... therefore NiMh in high capacity such as 1500 mAh and up - have really only job is to power low demand stuff like clocks and similar. You can power other higher - but the battery soon tells you its being pushed.

In voltage - NiCd and NiMh are basically same .... but charging is slightly different .... NiCd and NiMh chargers usually rely on Delta Peak detection. This means that when the cells get full - there is a slight drop in cell in mV's ... the charger detects it and cuts off. Problem is that NiMh has a poor Delta Peak point that many MNiCd chargers cannot work with ... and is why you are generally advised not to use NiCd chargers with NiMh and vv.

OP's problem is most likely that he has swapped low capacity NiCd for high capacity NiMh ... plus not having a NiMh charger.

There is no reason OP's radio shouldn't work with NiMh - but I would suggest getting lower capacity batterys .... at least 1/2 what he bought.... ie 1000mAh.

I find it strange that his charger refuses to charge the NiMh ... to the charger 6 x AA NiXX are all same except for that Delta Peak ... I suspect the charger may have a fault.

 

[Refueler]

I would expect any charger designed for NiCads to work perfectly well for NiMHs as well.

Yes but do not trust the full charge cut off ... as NiMh Delta Peak is hard to detect and different than NiCd.

The way to use a NiCd charger with NiMh is to revert to simple maths :

Stated capacity / amp rate of charger + 10% ... but not to exceed 1C rate.

Best is 1/10th to 1/5th C rate charge so lets make example at 1/5th C rate for his 2300mAh AA's :

1/5th of 2300mAh = 460mA

So charging of those batterys for 5hrs + 10% = 5.5hrs at 460mA ..... keeping an eye on temperature ... slightly warm is OK ... warm is still OK .. more than warm is STOP - they are not happy OR are full charged.

Serious users of NiXX cells have Temp sensors to monitor cell charging ... but thats another matter.

 

[wombat88]

Thanks all, I'm learning...

So:

The radio is fine, it is just a question of the charger.

The light does not come on. I used to have a habit of recharging the NiCds when I get home after any trip. Presumably my old NiCds needed it because the light would always come on. (Remember they were 18/19 years old).

I haven't tried to charge NiMh after more or less flattening them.

Is it possible that the increased wellie of the NiMh batteries is such that I have used far less power and the old charger thinks they are still fully charged?

Shall I try more or less flattening the NiMhs and then try charging?

By the way, the charger that came with these NiMh batteries (all Energiser) gets the batteries warmer than warm, almost warm/hot but it charges very quickly.

 

[coopec]

Maybe this has got something to do with voltage of disposables and voltage of re-chargables??

What voltage should a rechargeable AA battery be?

1.25 Volts

The proper voltage for AA/AAA NiCd/NiMh rechargeable battery is 1.25 Volts. These are great batteries.

Are AA batteries 1.2 or 1.5 volts?


The proper voltage for AA/AAA alkaline battery is 1.5V. ... The NiMH cells will be providing 1.2 volts throughout it's cycle use while alkaline cells go from 1.6v to 0.9 volts. Alkaline cells have a variable voltage which hardly makes them 1.5 volt batteries when they don't hold 1.5 volts for 80% of it's cycle life.



Can you get 1.5 V rechargeable AA batteries?




Yes, they are finally available. A company called Kentli has released AA and AAA rechargeable lithium polymer batteries that output 1.5 volts.

 

[Refueler]

Maybe this has got something to do with voltage of disposables and voltage of re-chargables??

What voltage should a rechargeable AA battery be?

1.25 Volts

The proper voltage for AA/AAA NiCd/NiMh rechargeable battery is 1.25 Volts. These are great batteries.

Are AA batteries 1.2 or 1.5 volts?


The proper voltage for AA/AAA alkaline battery is 1.5V. ... The NiMH cells will be providing 1.2 volts throughout it's cycle use while alkaline cells go from 1.6v to 0.9 volts. Alkaline cells have a variable voltage which hardly makes them 1.5 volt batteries when they don't hold 1.5 volts for 80% of it's cycle life.



Can you get 1.5 V rechargeable AA batteries?




Yes, they are finally available. A company called Kentli has released AA and AAA rechargeable lithium polymer batteries that output 1.5 volts.

OK .... lets clean this up .....

Rechargeable NiXX are rated at 1.2V .. with Dry Cells (non recharge) at 1.5V. But those are NO-load figures. Put both under same load and you will see the NiXX win every time .. with better stable voltage and a flatter discharge gradient.
It was not uncommon in the past where 'Dry Cell' powered items offered a rechargeable pack with ONE CELL LESS ... for that reason.

onto :

The radio is fine, it is just a question of the charger.

The light does not come on. I used to have a habit of recharging the NiCds when I get home after any trip. Presumably my old NiCds needed it because the light would always come on. (Remember they were 18/19 years old).

I haven't tried to charge NiMh after more or less flattening them.

Is it possible that the increased wellie of the NiMh batteries is such that I have used far less power and the old charger thinks they are still fully charged?

Shall I try more or less flattening the NiMhs and then try charging?

By the way, the charger that came with these NiMh batteries (all Energiser) gets the batteries warmer than warm, almost warm/hot but it charges very quickly.

I assume from that then - you have used the radio with NiMh and it works OK ?

mmm you would not use any different power ... but if the new cells are greater capacity - then you would have used less of their capacity % ...

Be careful flattening any battery .... I suggest not to take below 1.0 V each battery. Try to do each individually to avoid over discharging one or more.

Warm to Hot ... not unusual and this indicates batterys are full ... depending on the brand of battery - quick charging can be OK - but cheaper could suffer shortened life. If the batterys were supplied with the charger ... you would hope all is good ....
Personally I prefer not to quick charge any battery unless really necessary. Lower rate charging can increase life span. As an RC Modeller - I have a bench with a number of programmable chargers to cover most all battery types.

 

[wombat88]

Yes radio fine with NiMH. I am currently trying to run them down to roughly 25% and then see what happens with the charger.

This may turn out to be user error (blush). I have got so used to ancient NiCad rechargeables going virtually flat quickly that the performance and behaviour of the new ones may come to be something of a surprise.

 

[Refueler]

Yes radio fine with NiMH. I am currently trying to run them down to roughly 25% and then see what happens with the charger.

This may turn out to be user error (blush). I have got so used to ancient NiCad rechargeables going virtually flat quickly that the performance and behaviour of the new ones may come to be something of a surprise.

You probably will be surprised .... good luck.

 

[coopec]

The manufacturer of my blood pressure monitor specifies alkaline disposable batteries.

 

[Refueler]

The manufacturer of my blood pressure monitor specifies alkaline disposable batteries.

Many items do actually .... based on low power demand and lack of voltage drop. The alkaline will provide slightly higher voltage than the rechargeable .... as long as the amp demand is low.
But as soon as you start to run motors / demand a little more amps (actually mA's) - the voltage drop then favours the rechargeable.

 

[coopec]

Many items do actually .... based on low power demand and lack of voltage drop. The alkaline will provide slightly higher voltage than the rechargeable .... as long as the amp demand is low.
But as soon as you start to run motors / demand a little more amps (actually mA's) - the voltage drop then favours the rechargeable.

I think that's the message I got. The BPM is used infrequently and only for a short time and little load. Thanks.

 

[CliveF]

If the NiMh's very very flat to start with it could be there was not enough voltage for the charger to "see" them. I have had this happen with some of my rc chargers / batteries.
try getting a bit of charge into them with a separate charger outside of the radio , say 1/4 capacity, then put them back in and see if your base station fires up to complete the job.

Its a long shot as i suspect a 20 year old NiCd will not be that clever. However it is something for you to consider.

Regards C

 

[Refueler]

If the NiMh's very very flat to start with it could be there was not enough voltage for the charger to "see" them. I have had this happen with some of my rc chargers / batteries.
try getting a bit of charge into them with a separate charger outside of the radio , say 1/4 capacity, then put them back in and see if your base station fires up to complete the job.

Its a long shot as i suspect a 20 year old NiCd will not be that clever. However it is something for you to consider.

Regards C

Best way with that sort of situation - one of those general box desk chargers that take individual cells ... give them a few hours and then try the units charger again. If not - stick with the box job.