View Full Version : Dual Battery Necessary?

07-02-2007, 10:39 AM
I have been doing a lot of research, and like the idea of having two battery - so if one is bad you can still get back to the dock and aren't stranded. This is especially true since I just was left paddling back due to a bad alternator.

My question is this:

Is it necessary in my case - and does it by another....let me describe.

I have a 88 prostar and am running a Clarion M445 w/ a remote. There is no external amp on the boat. We like to play the music, but are rarely ever playing it for more than an hour without another person wanting to get a set and running the boat.

I have been investigating a Perko switch w/ the alternator protector, the relay style from Deisel's offical thread, and the charge isolators at boatersworld.

Do you think I need to run two battery is such a setup? why?

If it's so if one battery dies due to it being bad - the relay style will just cause the good battery die into the bad, correct? Is it better for me to setup the isolation charge one and be able to have dedicated batteries?

Thanks - any and all advice is appreciated.


07-02-2007, 02:39 PM
Forgot to mention that I do also have:
2 jabsco water pumps for an automatic fat sac system
1 normal pump to fill up an external bag that sits on the floor when wakeboarding...

Thanks for any advice - Ben

07-02-2007, 05:25 PM
My opinion is that it never hurts to have a spare battery and if you're using your boat for wakeboarding, the extra weight is good. We keep an extra and don't hook it up to anything so that if something does go wrong, we can at least get home (even without the alternator). It does need to get charged every so often.

07-02-2007, 07:56 PM
Yeah, I figure it's good to have one. I just am curiuos the best thing for me to do so that
1. I dont' have to maintain it
2. It's a best setup for my system

What is everybody's suggested 'recommended setup'?


07-02-2007, 08:19 PM
Another option is a portable power pack. I have a Xantex HD600 and it works great. Just used it all weekend to power all sorts of stuff at the lake, and at the end of it the thing still had enough power to jump start a friend's truck that had a dead battery.

I went through the same question when I added a 6 channel amp and some tower speakers to my X-1, but I decided to just get a good battery (Optima Blue Top) and a power pack. We often have the radio going for over an hour with the motor stopped and have had no trouble starting the boat.

07-02-2007, 08:21 PM
For what it's worth, I had only one battery in my '90 Prostar 190 with a radio/CD player and 4 speakers, no amps. I never had a battery die on me on the water, though sometimes I'd have to charge it after sitting idle all winter long. In the 9 years I owned the boat, I only had to replace the battery a couple times.

So, I believe you'll be alright with one battery - as long as it's a good one.

07-04-2007, 11:35 AM
Happy 4th...

This is what I decided to do. let me know if anything stands out that shouldn't be done.

First off, I purchased a Perko switch and a multi-battery charge isolator

I am going to (at least current state of mind) to wire the batteries to the 1 and 2 of the switch.
Then use the multi-battery charge isolator and connect the alternator directly to the batteries.

This way, the alternator will always charge the batteries - and keep both charged -- and - if I switch it to off on accident while the battery is running, the alternator will still be connected to the batteries so it won't get fried.

I was going to just connect everything to the out of the switch and not segrate the radio/starting/etc. Since my sound system isn't a major juice hog - and we don't leave the radio on for more than an hour w/out the engine running.



07-04-2007, 11:44 AM
Deep cycling a cranking battery is really bad for it and that means allowing the voltage to drop below 10Vdc. If that never happens due to never discharging it by using accessories or always having a trickle charger on it when it's not running, a second battery is not needed. You can also buy a battery with the most reserve, too. Something in the 850+ Ah (Amp-Hour) range should work well. Don't buy a deep-cycle battery for cranking- that's not what they're made for. Ideally, if you use two batteries, you want them to be very similar in charge state and capability. One old one and a brand-new sparkling high reserve battery isn't a good match if an isolator is used.


Before you buy an isolator, compare prices with a good car audio shop. Marine parts can sometimes be the same but are marked up more. It's not a distributor, pump motor or alternator so it won't need a Coast Guard rating.

07-05-2007, 12:47 PM
It's sounding as if it's silly for me to do the dual batteries. I already have most the supplies for it, but I do need to check the specs on the two batteries.

Would it make sense for me to do the above description, but always leave it on my primary battery (rather than both). that way I could switch to the other in a real emergency, and it will be charged?


07-05-2007, 12:59 PM
It is never a bad idea to have two batteries, however if you have one good one and dont exceed your "A" rating there shouldnt ever be a problem with the alternators internal winding melting. If you already have all the parts above I would go ahead and do it. Remember in the event it does happen you'll be turning a switch not waving for someone to come tow ya. Good luck

07-09-2007, 05:30 PM
I have a fresh Optima Blue Top that so far has never failed while sitting out cranking the tunes, w/external amp. I too thought about a dual battery set-up but so far I've not needed to go through the aggrevation. As a Back-up I always bring along a small portable jump starter which I have never needed.... If you have a good battery, it should easily take a jump from one of these handy gadgets. It's also nice to have when you get back to the truck and find out that you've left the lights on and need a jump just to pull your boat out!

But even today, after spending a week on the water without problems, I found the dual battery write-up by Diesel. (attached) Because my buddy's Crown has a dual set-up with Perko and continues to still have problems with his set-up....

If it were me, I would go with the isolation switch....... read on....

07-09-2007, 09:01 PM
Yup - that is the dual battery writeout I was referring to earlier.
What does your buddy's Perko setup consist of? Did he direct wire the alternator w/ an isolator - or does he use the perko itself to switch the alternator charge?