Professional Mariner Chargers

I have the ProSport Series and it works very well, but it is an onboard charger (confused with your not wanting it affixed comment). I suppose you could rig it to work as a portable charger, but defeats the purpose. They are very light weight

 

I've owned two ProMariner ProSport chargers and they both crapped out in less than a year.  My experience may not be common, but I'll never buy another ProMariner charger.  I now own two Minkota chargers, one has been going strong for 5 years, the other close to two years.  If you're not going to keep the charger on the boat you're asking for problems hooking up (and unhooking) your batteries, especially if they're in a confined space, but if that's your plan, why not just buy three cheap 2 amp 12 volt chargers for $25 each? When they crap out, just buy another.