Minimum amps for battery charger/maintainer?

I bought a 0.5 amp one. It wouldn't charge properly. Status would change between charged and charging every 30 seconds. Had to take it to a battery shop to get it properly recharged. This was after a full discharge after a parasitic draw overnight.

 

Seems low to me even for a trickle/top-off maintainer.

I'd get a 5A at a minimum, preferably 10A.



Also as an aside, I'm a believer in not storing batteries on a maintainer. For my camper that sometimes sits for long periods, I put a terminal disconnect switch on it. Charge the battery to 90%, unplug the charger, isolate the battery from the system. Keeps the parasites away from the go-juice.

 

If you have an AGM battery you will need a charger rated specifically for it, normal trickle chargers can't maintain them properly and will damage the battery sounds like you may have been having that issue.

Most AGM's require 14v charging and most chargers (to include alternators) only put out about 13v tops.

 

Recovering from a full discharge with any trickle charger is going to take a while, you want a 5-10A battery charger to do that.

Other than that, I've used the 1.5A trickle chargers for a long time and they work great.