How to best charge boat batteries when cruising around?

[qwiketz 10+ year member]

Hi guys. I have a boat setup with a dual battery setup and a 70 amp alternator. When I’m parked on land I can just plug it in. My question has to do with is there a good way to charge these batteries after I’ve been sitting playing music for a few hours? It is my understanding that alternators put out as much as there is a need. In this case there isn’t a lot of amperage required when the boat is crusing without the stereo on, but I would like it to recharge my depleted batteries.

what I’m getting at is if the batteries are depleted, would the full 70 amp output be used until the batteries are recharged? Would going to a 150 or 200 amp help the situation or just cost me horsepower with little benefit since there has to be a load?
Thanks!

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[THATpurpleKUSH 5,000+ posts]

Use the alt to charge the batteries. Boats always come with tiny alternators so upgrading would be a wise choice.

What used used to do was use a dedicated starting battery and then a huge deep cycle for the electronics.

Start the boat on 'all' or the starting battery and keep it on 'all' when under way. When it's time to relax, switch to your deep cycle so you aren't risking draining the starting battery.

You could also look into a solar charger to assist when the engine isn't running.

 

[qwiketz 10+ year member]

The solar one is interesting. I was also thinking of getting one of those small battery packs in case I do end up killing things or getting it pretty low.

min currently running two good size batteries but with 3 amps, it pulls some serious juice if I have it cranked up.

 

[Popwarhomie 5,000+ posts]

Get a battery isolator and run the stereo off the isolated battery.