dual battery questions

[94OMC]

Hi,
I bought a used boat that has 2 marine batteries and a 1-2-both-off switch. Battery 1 is a deep cycle-starting battery (looks like a wal-mart special), while battery 2 is a yellow-top Optima battery. Is there any advantage or strategy when it comes to utilizing the batteries and switch? Can I just leave the switch in "both" mode?

On the other hand, I guess it would be nice to have a fresh battery for starting after sitting at the sand bar listening to music for a couple hours. In this case, should I use the Optima for music and the deep cycle-starting battery for starting?

Is it necessary to upgrade the alternator when using 2 batteries? How could I tell if this has already been done?

thanks

 

[Don S]

Re: dual battery questions

Moving to Electrical & Electronics forum.

 

[PondTunes]

Re: dual battery questions

This thread should help you understand the different charging setups & how the switches work.
http://forums.iboats.com/showthread.php?t=228575

Couple Questions:

1) Does your boat have an outboard engine?
2) Is the optima yellow top a deep cycle battery?

If your engine isn't outboard you could upgrade the alternator, you should find out how much amperage your present one puts out first tho.

 

[94OMC]

Re: dual battery questions

The boat is an i/o 5.0L.

The Optima yellow-top is a deep cycle. I can double check the specs on both batteries later.

Thank you for the link.

 

[Silvertip]

Re: dual battery questions

Deep cycle batteries used for starting purposes are a topic of conversation that never seems to get settled but Optima is one manufacturer that says its ok. Now to the switch. With two batteries and a battery switch, neither battery is dedicated for starting as that function is determined by the switch. If you set the switch to BAT 1, BAT 1 runs everything including starting. If you set it to BAT 2, BAT 2 runs everything including starting. If you set it to BOTH, both batteries are on line. The idea is to make sure one battery or the other is always "saved or protected" for starting. So -- you switch to BAT 1 (or BAT 2), start the engine and then switch to BOTH. With the engine running, both batteries are being charged. When you stop for fishing, swiming, diving, or whatever, switch to BAT 1 (or BAT 2). Any accessories you are using will now draw off that battery, saving the opposite battery. When you are ready to go again, switch to the "saved battery" and after the engine starts, switch to BOTH. Never switch to OFF with the engine running unless you like to spend money on charging system parts. Leaving the switch set to BOTH at all times defeats the purpose of having it as both batteries are on line and both serve for starting and accessory use. No starting protection whatsoever.

 

[94OMC]

Re: dual battery questions

Thanks for the info.

Here's more info on my specific batteries:

Battery 1: EverStart Extreme, deep cycle/starting (675 marine cranking amps, 140 reserve capacity) - p/n 24DP-4

Battery 2: Optima yellow-top, deep cycle/starting (CA=870, CCA=750, AH=55, RC = 120) - p/n SC34DU

Which battery would you use as the "starting" battery? My guess is the Optima since it has higher cranking amps...

 

[Silvertip]

Re: dual battery questions

The Optima would be my choice. There is nothing inherently wrong with selecting BOTH when you start the engine. The only issue there is if you crank long enough you'll run both of them down and now you have neither as a back up. But if the engine doesn't start with two batteries, it certainly wouldn't start on one.