24 Volt Motorguide - Mixing two different 12V batteries OK?

[AdamW]

Hello,

I have a Group 31 12V deep cycle battery currently that I've used the past year on my Minn Kota 55lb 12V trolling motor.
I just picked up a used Motorguide 82lb 24V trolling motor so I need to get a 2nd Deep Cycle battery.
I was wondering if I could get a Group 27 12V deep cycle battery as the second one or must I get the exact same battery as the one I currently have? I assume I'm OK getting a Group 27 but thought I'd inquire first.

Thanks!

[CatFan]

It will work, Both batteries supply the same current, so they will run down at the same rate. The 27 will be deeply discharged before the 31 gets there so you'll run out of power when the 27 is done and the 27 won't last as long.

[billnorman1]

It would be best if you bought two new batteries. Most of us can't afford that but once every couple of years, but Walmart has some pretty good prices, you could get two good 29's here in the lower 48 for about $200. If you started off with two new ones you wouldn't be in the situation where if the 31 crapped out, you'd be pairing the new group 27 with a used one and then you still would be mismatched. The way I see it, sell the 31, buy two batteries, you're out maybe $100 more.
Too bad we're not related to The Donald, if we were we wouldn't even have to ask about the price, we could have one of the servants go to the store.

[Ann-Marie]

Expanding on what Cat said, if one battery discharges before the other, the good one will force current through the discharged one and destroy it rapidly. Batteries in series should be matched for capacity so they don't "fight" each other.

You can use a Trollbridge12X24 that puts the batteries in parallel whenever the trolling motor is not running. This will allow the weak battery to receive battery-to-battery charge and equalize their voltage. You get the advantage that the main motor will charge both batteries which will extend running time and improve battery life by reducing depth-of-discharge.