I have several SLA 12 volt batteries that have gone dead from lack of charging and simply sitting on the shelf. I've been considering keeping them on a string with a 13.8 volt DC source but don't want to "Charge" them. Merely want to keep them topped off. What would be a good amperage to maintain them? I'm thinking 20 mA to 200 mA. Advice please? Or redirect my thinking if you have a better solution.

These batteries just sit on the shelf waiting for a project or a use. If they're not charged every so often, which I often forget to do, they go dead. Need help stopping the bleeding (of voltage).

Thanks.

 

I would suggest that to apply 20mA and it was used for a charge current to reactive the battery when it was dead, you can try it does it suit for your batteries.

You also could use two ne555 and a counter as CD4020 or CD4040 to set the a period of charge time to charge the batteries, like one hour to charge one minute, etc,.

because it is the light current, so you can just use general bjt to control the charge gate as a Base of bjt.

 

Generally the trickle-charge is done at around 13.6V, with the battery taking whatever current it needs to stay charged (which will be a small current for a charged battery in good shape).