Anybody have any input on running a back up battery or just hooking the 2 batteries in parallel? Does it make a difference? I am using them to run a TM with i-pilot and looking to troll all day. Also will my dual bank onboard charger charge them both if hooked in parallel? Thanks for the input.
I would personally run the batteries individually with a switch. Hooking them in parallel will cause a weak battery to lessen the lifespan of a good/new battery. I don’t see an advantage to hooking them together. With a switch its 5 secs to go to the other battery. If they are easily accessible your talking 1 min tops to change the wires over manually. Just my opinion though.
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Anybody have any input on running a back up battery or just hooking the 2 batteries in parallel? Does it make a difference? I am using them to run a TM with i-pilot and looking to troll all day. Also will my dual bank onboard charger charge them both if hooked in parallel? Thanks for the input.
I gather your talking about a 12 volt system here ?
I run 2 12volts on my TM (PD 55 USV2 with IP and have them hooked up + to + and – to – on a 16′ Lund with 40 hanging off the back and I can troll for 2 full days without charging.
Same voltage but twice the amps, last ALOT longer than just 1 12 volt.
If you are to carry an extra battery why not use it to your advantage 
While it works great, just note that if you have a bad cell in one battery it will take away from the performance of the system.
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While it works great, just note that if you have a bad cell in one battery it will take away from the performance of the system.
That holds true for any multi battery system.
I had my old 12v TM in parallel, worked great, except I had no onboard charger. I would hook both up together, no dinking around with switching wires when one goes dead.
Most larger boats and experienced offshore boaters have twin starting batteries that are wired to an A – B – Both switch.
Having that setup allows you to run off either battery or both batteries, thereby covering a whole range of failure possibilities.
There is also an OFF setting that allows you to eliminate micro-drain by cutting off all power while the boat is in storage.
IMO, this is the way to go, HOWEVER you have to understand how the switching system works and how it should be used. You should start using either the A or B battery only. This way, the other battery is isolated and kept in reserve in case you park the boat and something happense to drain the battery you were using to start.
But you also have to remember to occasionally run on the “both” setting to keep both batteries fully charged. I usually do this on the last run of the day back to the marina, then I turn the master off.
As a note, I do NOT keep my boat in the water, it’s in dry stack. If you keep your boat in the water and have an auto bilge, it should be direct wired or on its own circuit so it cannot be disabled by the master.
Grouse
If you decide on running Parallel, I would buy 2 NEW identical, batteries!!
you will avoid what most have posted above.
You will be much happier running Parallel!
12v I assume.
I would hook it up to both with a switch, so it only uses one at a time. Then put all of your electronics on the other. If you need more juice, just flip the switch and use the electronics battery. Plus you will have your electronics, livewell, and all the other stuff off of your starting battery. If you drain both in one day of fishing then you really should look into a bigger TM or bigger batteries, or both.
If you do wire them in parallel, only use one bank of the charger to charge both of them. Or undo your parallel wiring and use both banks to charge. But don’t do both banks if your batteries are wired in parallel.
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