I am in the process of adding a third battery to my 353 to extend the "tune time". I have a typical 353 setup, Dual Batteries, with three switches (an on/off for each battery and a switch to tie both batteries together). My question is what is the best way to wire in the third battery so that it will charge off the alternator and when connected to shorepower? Any help or recommendations would be appreciated.

Thanks
Double Dealin'

PERKO website has all the diagrams on line--you can compare and download the right one--

WWW.PERKO.COM

Poorsche

Wire it in parallel with the current "house power" battery (+ to + and - to -). Make sure both batteries are of the same type (deep cycle, combination or cranking) and the same size (27, 31, whatever). That way, whichever engine alternator or battery charger charges up your current house battery will bring the new one up with it. If you have a 3-stage charger, you may have to re-set the current settings to allow for the increased capacity. Whatever you do, do NOT combine gel cell or AGM batteries with conventional flooded-cell batteries. The maximum charging voltages are different.

If you are not sure which battery is your house power battery, turn your stereo on, and turn on each battery switch, one at a time. Whatever you do, don't sit with the stereo blasting and the combiner switch on. You can drain all 3 of your batteries that way.

C_Spray - Thanks for the info. I was looking at using an Optima as my third battery in conjunction with the flooded cell battery. What are the risks, Boiling one battery while the other is still charging?

It depends on what voltage your charger and/or alternator are set to. Sealed gel batteries should be charged to at least 13.8 volts, but no more that 14.1. Absorbed glass mat (AGM) batteries should be charged to at least 14.1 volts but no more than 14.4 volts. Conventional flooded batteries are slightly higher yet, depending on the lead alloy. Each type of battery also has a different saturation charge duration.

If you set your chargers to a voltage low enough to protect the gel battery, your conventional battery will not be anywhere near it's full potential. If you leave your chargers high enough to fully charge the conventional battery, you will toast the gel battery.

Not so simple, eh?

Mixing battery types is far worse than mixing radial and bias ply tires.

Thanks for the info. Once again, a simple project becomes much more complicated.

If you put the 3rd battery in there in parallel, would the stock 60A alternators be enough? If you had 2 completely drained batteries I wonder if that would overload the alternator. Could you upgrade one of alternators that had the 2 batteries on that side, or would that cause a problem when the 2 circuits were combined (All position on a battery switch)?

I would like to add a 3rd battery in parallel to one side, so when anchored I could have 2 house batteries on for the fridge and stereo, and have 1 fresh starting battery on the other circuit.

Thoughts?

jaybird, that is my question as well? The same goes for the on-board factory shore power charger. Will it be able to charge all three batteries sufficiently? I am looking to do exactly what you stated, add one battery to the house side so that I have, theoretically, twice as much reserve for the accessories, mainly the stereo. Any thoughts out there?

You won't hurt the alternator(s) or the charger - they will just take longer to get everything back up to full charge. If you stay with the same style battery (Flooded, gel or AGM) for both your house bank and your cranking battery, you will be able to combine the switches when you are running and use both alternators to charge the house bank faster.

If you use gels or AGM batteries for the house bank, you will have to set your alternator and charger for that bank different to the alternator and charger that take care of your starting battery, and should NEVER combine the banks (unless it's an emergency).

You guys are both on the right track. Just buy another battery identical to your current house battery, and hook them up parallel (+ to + and - to -), and you'll be all set....

The reason I ask about overload, is that on my old boat with a single engine when I ran the stereo (800 watts RMS, drawing probably somewhere around 15-20 Amps), and I was underway, the alternator would get ultra hot. I mean it would smell, and you would burn your hand if you touched it. It seemed to charge ok if I just had a dead battery without using the stereo. Using the stereo while the boat was running seemed to be a problem, even when the battery had a decent charge. Another friend had the same thing going on too. I never figured it out before I got rid of the boat.

I am wondering if my current boat with twins would have enough power to run the stereo without killing the alternators.