Great article Tartuffe. Thanks for posting it. :clap: About the only thing I could add to it would be the recomendation to always use identical batteries in a dual battery situation. That way the drain from them and the recharging of them would be easier to manage. Not always pratical for sure, but better than having two dissimilar units.:head:

Two battery systems when properly set up are terrific and provide excellent security and back up .

I've run boats with one & two battery systems and currently run my V21 with one.
New, proper size, and plan to replace every 4 years. For many boating situations, I believe a single battery is fine.


That said, I considered a 2nd for the V, and always interested to listen to other ideas.

i just put new battery's in yesterday, two 27m-xhd from interstate battery's. 850 cca, 1000 mca
Boat started right up after a long winter nap!!
switch #1 to first battery, #2 to 2nd battery, i also have a wire running to the cabin for all power to front, that comes off the 2nd battery, also a 1100 gal bilge pump to each battery.
Start boat on #1 battery then put on both to charge, then when fishing i stay on 2nd battery all day, so if i kill it i just switch #1 and start and go. but always on bth batterys to charge on way in.
has always worked for me with no issues! but agree to have same batterys for same charge and discharging.
my pumps go right to a battery, 1 on #1 battery and 1 on #2 battery with no fuse and one mounted a little higher then the other. this way one will work till first battery dies the the 2nd one will take over till that battery dies.no problem for a burned out fuse if none there.
I also have a 700 in the rear and a 500 that are hooked up with manual switch to pump anything i see before the auto 1100's do, they just for when boat is on the morring

Question guys, I have a two-battery system with dissimilar batteries, one is a starter and the other a deep cycle. I keep them in parallel most of the time but when I am bottom fishing I switch to the deep cycle. I have sat for more than 5 hours without ever having an issue with multiple items drawing power.

Are you guys with duplicate batteries running deep cycle or starting? If starting batteries, how many hours of radio/stereo/live-well pump/occasional lights time are you getting out of a battery?

I ask because I am about to go with new batteries (been 4-5 years) and would like similar batteries but question if using deep cycle for starting works. Alternate is using starting batteries for long-draw applications.

i have never seen a need for a deep cycle battery, except for a trolling motor or other high use item. i have used regular battery for everything else, but nothing is of high demand.
but i also use electric reels for cod fishing and have always used a friends deep cycle for that.

so the answer for you is if you are using electric trolling motor, live well all day or electric reels, or other high demand stuff, then yes you need, but if its just everyday stuff then no

Both my downriggers are electric, so lately I've always gone with deep cycle batteries (commonly called Marine batteries). But truthfully, I've used automotive batteries many times for many years with no problems. The deep cycle batteries are really only good for applications where you really discharge the battery. (Like Downriggers, Reels and Trolling motors) Otherwise you'll do just as good with an Automotive (car) type of battery.

Sounds like I shouldn't have a problem with a marine radio/stereo/livewell for sevral hours at a time. Good to know, thanks.

The radio and the stereo both are electronic units and don't draw much current. The livewell, on the other hand, has a pump that draws significant current compared to the other two. I would run the livewell off a different battery than the one that I use for starting my engine.

Subscribed! I'm stuck on this thread like glue. Doesn't somebody want to draw a schematic for showing bus bar hook UPS and that sort of stuff? LOL!!!!

Thank you everyone for all the helpful tips! I hope to be finishing this project this weekend I've been busy working. Damn work getting in the way of my fun!:beer: