Dual batteries without an isolator?

[vortech347]

I did not have much luck searching on this.

My question is would there be any drawback to running two identical batteries without a perko type switch or isolator?

My boat is a 99 Sport Nautique with the single battery in the bow under the front seat. I have a relatively large stereo and we do quite a bit of lake lounging with the stereo on but not at very high volume.

We have only run the battery down low enough to not start the engine two times in 15 years. For that reason I carry a jumper battery in the boat.

I want to run two batteries and will just buy two AGM's of the same size and put one in the stock location and one under the observers seat pushed forward and wire them in parallel. That would give me double the reserve capacity and considering the low volume that we listen to music at I should never have a no start situation.

I already have two amplifiers mounted under the observers seat on the inside wall so adding a battery switch there is out of the question. That's the reason for my inquiry.

I always plug a charger/maintainer in when storing the boat so the battery is fully charged each time we head out.

My line of thinking is the batteries will always be a matched set similar to what you should do with diesel trucks that have two batteries without isolation.

I'm just wanting to know if there are any other issues that might come up.

[MLA]

It will just take twice as long to pull the battery level down as you will be doubling the Ah, but it will be pulled down and there will be no fresh battery in reserve. Spend the extra $30-$45 for a dual-battery switch IMHO.

[scottb7]

For me the only reason to have the switch is peace of mind. When you are parked you isolate one battery. Then no matter how long you are parked you will have the isolated battery to start you back up. Whenever engine is running you put on both to keep em topped off.

I am a paranoid type so for me I got to have the switch. Plus at beginning and end of season there is no one on the lake to jump me off or tow me home.

But as you know the reality is that with 2 batteries - even somewhat discharged - the likelihood of not getting the boat started is pretty darn slim....

[pe4me]

Save your $ and buy a normal battery rated for use, Interstate has always pointed me in the right direction. Through business (skid steers, trucks, boats) they have always been knowledgable and friendly. I was even introduced to the "refurbished" rack that maybe used but has been rebuilt to the new spec and gotten more battery for the $.
If the goal is to avoid carrying a jumper pack and worrying about draining to low, the switch seems to be the easiest solution. The previous 2 boats required the jumper pack, but importantly required me to ensure it was charged and to be sure it made it to the boat. At the end of a long day it sucked to lug it around here and there. Switch for me = back saver.

[kend]

switches are nice; you could set it to pull from both. I always take a jump box because its lighter than another battery and has a air station for toys (ya, tubes sometimes) and a light, and a usb for charging phones...I can't live without my jumpbox

[vortech347]

Save your $ and buy a normal battery rated for use, Interstate has always pointed me in the right direction. Through business (skid steers, trucks, boats) they have always been knowledgable and friendly. I was even introduced to the "refurbished" rack that maybe used but has been rebuilt to the new spec and gotten more battery for the $.
If the goal is to avoid carrying a jumper pack and worrying about draining to low, the switch seems to be the easiest solution. The previous 2 boats required the jumper pack, but importantly required me to ensure it was charged and to be sure it made it to the boat. At the end of a long day it sucked to lug it around here and there. Switch for me = back saver.

I was thinking AGM because one will be going under the observers seat so I thought it would be less likely to spill, leak, etc. Even though I've never had a regular one leak before it was just a thought.

I don't intend to stop carrying the jumper battery as to me that's cheap insurance. I mainly wanted the extra runtime and not have to use the jumper battery if we wind up on the lake for extended periods of time without running the motor.

The switch I would do later on when I upgrade one of my amps and add a 100 amp alternator upgrade. So I plan to do it just no this year.

[Brichter14]

Go with a switch. This alows you to isolate one battery and be safe with a backup. It also allows you to select which battery you want to charge at a time. For 40$ there is no reason not to.

[2001SAN]

Don't bother connecting the second. Switch them if you get stranded. Simple!

D.

[sodbuster88]

Getting off the subject of the switch a bit...but still pertinent, check this out for some 101 on batteries, alternators and sizing for amplifier requirements ( nothing new, but good fundamental information ). Armed with this you can, decide for yourself...

http://www.termpro.com/asp/pubs.asp?ID=117

[barefootinjimmy]

Years ago when second batteries were not even considered, I had monster stereo systems (700W - 800W systems). To avoid this issue, I took my stock alternators to an alternator shop to increase the output. I think the stock alternator has a 51Amp output, and I increased it to 90Amp output.
If the alternator can keep the battery close to full capacity when the engine is running, it battery will last longer. This will not make the battery last forever. I never left the stereo play for hours without the engine running, but I never was stranded.
I can only stay stationary so long before getting bored, and wanting more play time behind the boat.

Just a thought.

[pe4me]

I think having a battery properly secured would be fine even in hard driving conditions, but that is just my experience. A sealed type may work for what you are doing depending what you are doing and what the battery's home looks like.
The average guy (probably me) understands and can follow along in a electronics discussion and sort through the info on articles that are posted above. I guess for me, having a vendor and known resident battery expert advise me to save my money unless I am competition stereo guy (which I'm not) or had other unique voltage needs, makes me wonder how many guys are putting way more $ into batteries they really dont need.
Also, when I bought my boat from White Lake Marine, the guys there also indicated I could just use the good old interstate battery for my needs and not have to worry. They didn't try to upsell me or talk me into something I didn't need which also tells me that WLM and the guy in Wisconsin were on the same page.
It is probably worth noting my system has the 2 stock amps + WS syn4 powering the 2 added rev 10's. I thought 3 amps would be pushing it and while both said I maybe at the upper limits, as long as we were not cranking for extended beach sessions I would be fine...and so far they have been right.
Just something to consider as you make your decision-