Adding another battery

NateRW21

New Member
Mar 17, 2008
201
Michigan
Here's my situation, hopefully you guys have some good ideas for me!

I've got a 160 Bow Rider which I've already installed a nice sized in-boat stereo, and it will soon be getting a wakeboard tower with speakers. These tower speakers will require an additional two amplifiers on top of the one already installed. Obviously this is a tremendous requirement for power!! I'm going to upgrade to a 140amp alternator when I do the tower; that will cover me while I'm under way. My issue now is if I want to run the stereo while having fun on the beach. I currently have an Optima D34M Blue top installed (870CA, 120RC, 55AH) as my only battery. With the current stereo (not including tower speakers) I can run for around 45min-1 hr, 15min (depending on volume) and still be able to start the boat. But, I need more!! So I intend on installing another battery. I'm debating installing the Optima blue top D31M (1125CA, 155RC, 75AH) as the second battery and using this one as my "House battery" per-say.

Given the above info, how would you guys advise I hook this up? The batteries will be on opposite sides of the boat (one under each stern jump seat), and I have an Xantrex charger that charges up to three batteries (or banks) separately... so it's important that once the boat is powered down, these batteries stay isolated aside from ground. And of course, I'd certainly want both batteries to charge from the alternator while under way. I'm looking at this as insurance that my big stereo doesn't leave me short on cranking power!

Thanks guys (and gals)!

ps... don't worry, I'm also going to be bumping up to at least 2ga wire when I do this; I know plenty about electrical principles/requirements... just haven't dealt with a situation such as this before!
 
What I would recommend is a deep cycle house battery (not a combination starting/deep cycle) and a battery switch and a combiner. The best way to do it would be to add a battery isolator or combiner to the circuit and thus keep the batteries separate but still chargeable by the alternator when under way.
Blue sea has a lot of good resources for doing this.

http://bluesea.com/viewresource/69
 
Okay I checked that out... I appears as though when the switch is off with that set-up, the isolator can not combine the batteries correct?

My main issue is keeping the batteries isolated when the boat is not in use so my battery charger can maintain each battery separately.

IF that's the deal, I think you gave me a solution!! Thanks!
 
With the switch in the off position the batteries are isolated. If you turn on your battery charger the system should act just as if the engine was on. The batteries will charge normally. I am connecting my chargers directly to the batteries.

You do bring up a good question about the charger. I had not thought about it until now. I do not see a problem though.

The way the ACR works is that it senses the combined voltage of both batteries. If the combined batteries are below 12.7 volts the relay opens isolating the batteries. If they are above 13.5 volts the relay will close combining the charge to both bateries from a single charge source the alternator.

If both batteries are receiving a charge voltage the relay will sense the charge voltage and if above 13.5 it will close. No problem.
 

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