Hi
I have a very nice one (have used it for 12 years now) that has protection against pretty much all fault conditons, reverse polarity, short circuit etc. It also has a turbo switch to give very flat batteries a boost in order to start charging. The only problem is that the circuit is set to provide 4A. It starts in constant current mode and then switches to regulated voltage mode to avoid overcharging. It can float a battery indefinitely. Perhaps someone clever here will modify the output for you, I am not that bright.
Cheers
Andrew