Adding second battery?

[davesparks2001]

I've just been reviewing some previous posts about adding auxillary batteries, switches, relays and such. I'm definately interested in putting a house battery on our pontoon so we don't risk running down the starting battery while we're using the stereo and accesories. My question (maybe I didn't read enough existing posts) is, since we have an outboard motor, I'm guessing there is not much there in the way of an onboard charging system (alternator) so is there any reason to put an isolation relay or switch between the batteries? For all practical purposes, wouldn't I be just as well off wiring the accesories to the second battery (deep cycle marine?), leaving the ignition circuit on the starting battery and installing a 2-bank charger to recharge them when I get home? I tried to research this to avoid asking a question that I'm sure has probably been dealt with numerous times a season since this site came on line, but it looked like most of the other posts I looked at we're dealing with I/O motors with alternators. Sorry if this annoys you guys that have been around a while. Thanks, Dave

 

[Silvertip]

Re: Adding second battery?

Your first duty should be to list the electrical items you have on your boat and then decide if it is really necessary to do this. Until I see something like stereo with a 400 watt amp or trolling motor, you don't need two batteries. You also need to tell us what engine this boat has as alternator output is key to all of this. Until we know what you have a portable jump start unit may be all all you need for insurance. Why spend a couple hundred bucks or more if you don't need to. Size of the lake/impoundment you boat on also has a bearing on what you do.

 

[davesparks2001]

Re: Adding second battery?

Sorry Silvertip, I was reading a bunch of existing posts and got caught up in the moment. Our pontoon has a 90hp Force (by Mercury) outboard. This is my first outboard so I'm just assuming there is no alternator? We don't have a big honkin sound system on board and currently don't intend to add one. Just a basic am/fm/cd player with 4 speakers and a gps/chartplotter/fishfinder. I'd just like to know I can keep the music going for hours on end without fear.

 

[Silvertip]

Re: Adding second battery?

Yes you have an alternator but you don't see it because it is part of the engines electrical system and located under the flywheel. The fact that you HAVE an alternator is one thing. The output capacity (charging amperage) it can deliver is quite another. I have no idea what year this motor is or what it's alternator output is but someone will be by to fill us in. Fact is that most older outboards had alternators sized to keep the starting battery charged. They were not intended to keep two or more batteries topped off without some combination of devices you have become interested in. Understand that even if you add the battery and the necessary switch equipment, if you deeply discharge the house battery, you still need an on board or portable charger that plugs in at the dock to charge that battery. Assume you sucked 40 amps out of the house battery. If the engine had a 16 amp alternator you would need to run wide open for over two hours to charge that battery from the engine plus however long it took to bring the starting battery back to full charge after starting. Your best insurance is to install the largest starting battery (dual purpose - starting/deep cycle) and keep the engine tuned. If you still want the second battery, add a dual battery switch. Move every accessory including the large starting battery cable to the COM terminal on the switch and then use whatever battery you wish. The switch provides the absolute best flexibility, simplicity, and at the least expense. To determine if you need to do this, turn the radio on in your car and leave it on all day. If you have a reasonably sized battery your car will still start. That engine requires far more power than your 90HP outboard.

 

[lncoop]

Re: Adding second battery?

Dave, as Silvertip says, provided your engine doesn't require extra time on the starter one battery will be plenty (assuming you won't be running the fishfinder all the time). I start a ninety horse Merc and run the stereo all day off the same battery and have never had an issue. I do carry a spare battery, but that's only because I had intentions of adding a switch and running a two battery system, but after two years of no issues I decided the extra expense and work weren't warranted. Now I just leave the second battery in there with the first one and leave it connected to the on board charger, but it only gets used for other projects. Speaking of on board chargers; if you don't have one I'd strongly encourage you to get one. You'll remember me fondly every time you plug it in.

 

[davesparks2001]

Re: Adding second battery?

Thanks guys. Again, Silvertip, I'm remissed in my duties. The outboard is a 1998 model. I'll try to stop myself and take time to be more articulate in future threads, I appreciate you guys putting up with me. If I ever decide to add a 2nd battery the switch sounds like the best idea for my humble party barge but it sounds like overkill at this point. I'll definately add an onboard charger, of course thinking fondly of my forum breatherin every time I plug it in. I'll consider making the charger a two bank unit just in case I ever decide to add a trolling motor and I'll ponder a bit about putting another battery on there as a back up, or perhaps a nice jump start unit. Thanks again guys.

 

[jjohnson120]

Re: Adding second battery?

I'm going to have to kindly disagree, and say that if you have the opportunity and can afford a second battery, I would do it. There is nothing worse than being stuck out on the water with a dead battery. In the grand scheme of things, at some point something will go wrong, and in the case of a second battery, it's a cheap insurance plan in my opinion. At the very least if you have a battery I'd throw it on the boat with a set of jumper cables. You just never know. I went ahead and wired mine in like you were mentioning above this year after just carrying the battery and cables around all last year. It was nice when I needed it, but now is much nicer as when I'm anchored I use one battery to listen to music, and the other to start the boat. This along with an on-board charger and you shouldn't ever have to worry about having a dead battery.

To me that's a nice cheap luxury.

 

[davesparks2001]

Re: Adding second battery?

Thanks for the additional input. I agree with everything I've read here. I don't really see a legitimate "need" for a second battery in my circumstances, but I can sure see where it would provide some peace of mind. Until I get our old boat sold, Momma says I won't be buying anything, lol, but, I'm kinda thinking about incrementing one step at a time toward the "feel goods" of having the back up. I'll buy a two-bank on board charger first. Then add the second battery and switch as the liquid assets are more availble.

 

[River_Lizard]

Re: Adding second battery?

I'm on the side of a secondary battery. Leave your main battery for your outboard, when you shut your engine off switch over the the secondary and run radio, depth finder, nav lights, etc... When you're ready to pull anchor, flip it back over to the main battery and you have no worries about draining your outboard battery during the day. I installed a selector switch on mine this winter, but before that I just carried 2 batteries and I've had twice that I need the second one.