# Trying to understand AA batteries and their capacity

Discussion in 'Power Electronics' started by MKANET, Jul 15, 2012.

1. ### MKANET

26
0
Jun 3, 2012
Im curious, if two batteries (AA batteries) can make an electronic device last 6 hours, is it as simple as adding two more of the same batteries to make the same device last 12 hours; considering the electronic device draw a constant/same load continuously.

I would prefer to know the simple answer to this, if possible.

2. ### MKANET

26
0
Jun 3, 2012
I tried reading other posts in hopes I could figure out the answer to my own question; but, I'm still not sure. Not sure if that would make the voltage go higher or there is a way to make the voltage the same; except make it last twice as long.

1,114
159
Aug 13, 2011
Theoretically, yes, you can double the capacity by doubling the number of batteries in parallel. This will not alter the available voltage as would be the case if you added batteries in series.

I said theoretically because there are some problems associated with putting batteries in parallel so it's usually not done; a larger battery is used instead.

All you ever wanted to know about alkaline batteries:

http://www.duracell.com/media/en-US/pdf/gtcl/Technical_Bulletins/Alkaline Technical Bulletin.pdf

Last edited: Jul 15, 2012
4. ### donkey

1,293
56
Feb 26, 2011
if you want more time than you could try upgrading the battery to a C or D... you could also try the longer lasting batteries (Lithium for example)
but yes theoretically you could just duoble the batteries to provide more mah.

5. ### gorgon

603
24
Jun 6, 2011
Even if the theory say this is possible, it is not practical in real life. To manage this your batteries needs to be exact equal in voltage. If not the battery with the lowest voltage will 'short' the one with the higher voltage and draw power from that until the capacity/voltage is down to the low level. This will in the best case waste a lot of the capacity, in the worst case the batteries may run away into heat and maybe overheat. It depends on the battery techology.

In both cases the you will not get the double capacity you wanted.

One way to do this is to isolate each string of batteries with a low drop diode, connected in a common point that is the supply voltage. This way each battery(string) will supply it's power in parallel with the other, without feedback to the other batteries.

The voltage will be a bit lower, depending on the diodes in use, but you'll get max power out of the batteries.

TOK