Batteries in parallel = higher mAh?

Thread Starter

mike_canada

Joined Feb 21, 2020
239
I was wondering. If I took a handful of 9V square batteries and connected them in parallel (where all anodes (+) are connected together and all cathodes (-) are connected together but no anode or cathode join each other) would the mAh value be the sum of the mAh values for each battery with the voltage the same?

And is it a bad idea if I left these batteries connected this way for a long time if they are not in use?
 
Yes - the mAH capacity would be the sum of the individual batteries.
No - there's no problem with leaving them connected like this.
It's important that they be more or less identical, though. Most especially you don't want to mix different chemistries like alkaline and Le Clanche or lithium.
 

BobTPH

Joined Jun 5, 2013
5,743
And all of them should be at nearly the same voltage when they are connected. Otherwise, a oarge current would flow between them.
 

DickCappels

Joined Aug 21, 2008
9,297
The two batteries should have the same chemistry (carbon-zinc, or alkaline) Putting batteries of the same chemistry in parallel is a lot like making the anodes and cathodes look like they are larger electrodes on the same battery.
 

WBahn

Joined Mar 31, 2012
27,389
I was wondering. If I took a handful of 9V square batteries and connected them in parallel (where all anodes (+) are connected together and all cathodes (-) are connected together but no anode or cathode join each other) would the mAh value be the sum of the mAh values for each battery with the voltage the same?

And is it a bad idea if I left these batteries connected this way for a long time if they are not in use?
Yes, with caveats. As already noted, the batteries should be as identical as possible. This includes being the same same state of charge (which, in practice, means that they are new, otherwise you have no idea what the individual states of charge are. Try not to mix batteries from different manufactures or even different product lines from the same manufacturers since the discharge characteristics will be somewhat different. This may or may not be a major issue, but will likely at least result in the effective mAh value for the ensemble being less than it would if they were truly matched.

As for leaving them connected in storage -- in theory, it shouldn't matter, but again in practice it might make a slight difference in most cases and a big difference in cases where one battery goes bad. I that situation the bad battery might just ruin the other batteries, but in extreme cases the good batteries could dump enough energy into the failed battery to cause a melt or a fire. I would expect the likelihood of this with batteries like 9 V, but with car batteries or submarine batteries, it would be more of a concern.
 
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