Rechargeable batteries

  avesnes1 22:19 18 Sep 2010

I wonder if anyone in this forum can enlighten me as to why AA & AAA rechargeable batteries are rated at 1.2volts output whereas ordinary AA & AAA batteries are rated at 1.5volts?

(My query is based entirely on ignorant curiosity.)

Thanks in advance for any guidance.

  QuizMan 22:54 18 Sep 2010

I think it is because the 1.5 volts of a standard battery is the starting voltage and it reduces with usage. However rechargables of the nickel cadmium variety start at 1.2 volts and reduce very little from there.

  Fruit Bat /\0/\ 23:07 18 Sep 2010

Its to do with the materials the batteries are made from - the two different metals required and the Electrolyte between them.

The chemical reaction produces the voltage hence as chemicals are used up batteries go flat.

Ordinary batteries usually Zinc Carbon
Carbon get eaten away hence not rehargeable

Nickle Cadmium batteries the chemical reaction can be reversed hence rechargeable.

  avesnes1 11:59 19 Sep 2010

Many thanks for the answers. The reason that I asked is because I have in my garden a fox deterrent that runs on 6 AA batteries. When the batteries no longer operated the device, I measured their voltages at 1.1volts.

I was thinking about using rechargeables in the deterrent and then having noticed their 1.2v rating, I was wondering just how long they would last before needing recharging.

I had visions of them running down very quickly but Quizman's response suggests perhaps not.

A timed, controlled experiment is called for, I think.

  jakimo 14:21 19 Sep 2010

rechargables do not fully recharge every time.

Every time a rechargeable battery goes through a charge and discharge cycle it loses a tiny bit of capacity.
A rechargeable will have a longer life if recharged before it is fully discharged

  TopCat® 16:58 19 Sep 2010

Here's some
useful rechargeable info. TC. click here

  Bingalau 17:06 19 Sep 2010

I thought the idea was to fully discharge the re-chargable batteries before re-charging them?

  skeletal 18:07 19 Sep 2010

Different battery technologies respond differently to charge/discharge cycles; TopCat®’s link gives an outline.

For some strange reason, device manufactures seem to design their equipment to run at multiples of 1.5 V and as the voltage drops to multiples based on around 1.1, 1.2 V they stop working. Thus, a rechargeable battery(ies) is often close to the point where the device stops working. I had this problem with a camera; it shut down even though there was still charge left in the battery.

It is odd because so many people want to use rechargeables and it would be easy to slightly change the cut-off point.

Given that every piece of equipment will be different, I can only suggest you try it and see how you get on; you might just make it as the 1.1 V is a bit lower than the nominal 1.2 V of rechargeables. They may not last quite as long as you think though so may need more frequent recharging.


  peter99co 20:02 19 Sep 2010

A lithium Non rechargable 1.5 is best for a camera as it will last much longer. Bit expensive though.

  onionskin 21:34 19 Sep 2010

I understood that rechargeable batteries will give you all the current you want, but at a fixed voltage. Standard batteries will give you all the voltage you want but at a fixed current. Or is it the other way round?
Anyway, you can now get hybrid rechargeable batteries which supply a higher voltage, similar to a standard battery, (you can use them in clocks). Don't know how long they last though.

  Dragon_Heart 22:10 19 Sep 2010

They say they will hold their charge for about 12 months !

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