Electronic – Floating multiple sealed lead acid batteries in parallel


I know with multiple lead-acid batteries you should really charge them separately so that one battery doesn't try and charge another and waste power.

But that holds true for the main charging process.

What about the "float" portion of the charge?

I have a number of SLA batteries that I'd like to keep charged up. The initial charge of each battery will be done separately as and when they get removed from the bank and used, but between uses, when they have been fully charged, I'd like to have a single float charger to keep them topped up.

Is it safe to just whack them all in parallel with the one float charger, or would I need to have some form of separation (e.g., a diode per battery), or even an individual float charge circuit per battery? I'd like to keep it as simple and cheap as possible.

Best Answer

In theory it is OK to connect them in parallel with two conditions:

  1. Each battery must be in a state where it can be voltage charged. This is fine for lead acid batteries unless they are very run down. Very discharged lead-acid batteries have to be charged with fixed current until they get to a minimum voltage, then they can be voltage charged.

  2. The power supply is capable of maintaining the fixed float voltage.

In practise, I think it's a good idea to put at least a diode in series with each battery just because stuff happens. Of course the power supply voltage needs to be adjusted to get the float charge voltage after the diodes.