I use the simple method. If i know that i'm not going out for 3-4 weeks then i simply make sure the ACR switch is off (which it always is) and connect two trickle chargers to the batts, plug them into a gang plug, connect an extension cord and run it into the garage. Done. Hurts nothing, no issues and the batts stay charged. Some people will say trickle chargers don't do the job ... I say BS! They are maintainers and automatic only allowing a charge when needed.

I use the battery tender jr brand and they work fantastic. They have a quick connect harness that stays on the batt so connection takes seconds without even taking the box cover off. In fact that's the same charger H-D uses re-branded and i've used one of those for years on the bikes. I would average 5 years on a Harley AGM batt, almost unheard of, all due to maintaining.

There was a thread on WW a couple years ago where "G" (who has 5-6 batts) simply installed a bunch of battery tender jr's into a plastic box, hung it over the boat and plugged them in and his batts stayed perfect. His system has four ARC amps, three subs, six coax, tower speakers, two playback LCD screens, etc. You get the point. He did find afterwards that his alt couldn't keep them all charged so he added a Balmar 160a alt later.

Long post but that's the reason i don't see the need for a big onboard charging system. To me, and let me quantify this is just my opinion, they are just more for the bling factor. Somebody started adding them to wakeboats and now it's one of those must have options. Again just my 2 cents worth and opinion.