Battery Charging Question

I have a 24 volt trolling motor system with a 2 bank charger connected to the 2 batteries, so that is covered.  I do not use the gas engine too often because of where we fish so a couple of times the starting battery has been dead when I have needed it, I suppose that I drain it down from lack of use and it runs my 898 and the radio.  Is there a single bank charger that I can connect to the starting battery like the 2 bank charger to the trolling motor batteries?  What I mean is something that attaches to the posts (Not clamps like a battery charger) and they will not fall off, I could mount it, and the cord could be tucked away.  Something small that can be mounted but easily accessed when needed.  I could just plug it in when Iam charging my trolling motor batteries and not have to worry about any of them not being charged when I go out.

Thanks-Arlo