Hooking up two batteries

[Wish-I-Were-Fishn]

I have two 12 volt deep cycle batteries for my 12 volt Minn Kota motor. Can I hook them pos-pos & neg-neg to extend my running time, or will that make it 24 volts output?

I know I can charge them that way, so it got my to thinking about using them hooked together also.

[hoggs222]

+ to + and - to - will keep it at 12 volts. + to - and + to - will get you 24 volts.

[PerchJerker]

Hoggs is right on, and yes it will extend your running time!

[Wish-I-Were-Fishn]

Do other guys do this? I'm surprised I have not heard of leaving them hooked up together before.

On wilderness trips away from ac charging power, I would just run down one battery and then hook the other one up in it's place. Makes more sense to just leave them them hooked together doesn't it?

[BobT]

A lot of batteries are connected this way.

Two batteries wired in parallel (+ to + and - to -) provide you about double the current capacity without changing the voltage. It is about the same as using one battery till near dead and then connecting to the other battery. You're drawing the power from both batteries simultaneously so by hooking them together you can save the step of switching batteries.

There is a potential risk in wiring two batteries in parallel. The power supply will be limited by the weaker of the two. If one of the batteries is in poor condition it will drag the other one down with it. An extreme example is what happened to my diesel truck, which used two batteries in parallel. One battery developed a short-circuit and it destroyed both of them. At 1000cca each, it cost me nearly $350.00 to replace them.

Many use two batteries wired in series (+ to - and + to -) to power 24vdc equipment. Connecting two batteries in series provides the same current capacity but the voltages add together so two 12v batteries connected this way will provide 24v power.

Again, the total ability of the system is limited by the weakest link. If one battery is not delivering a full 12v, the total power will be sacrificed.

In either case, it is always best to start with both batteries new.

Bob

[Bullwinkled]

I always bring 2 extra 12 volt 7 AH batteries when fishing Mille Lacs 12 hour day on ice I have banana jacks on my Vexilar and Aquaview and then when on the ice I plug a battery in series with each one when I am settled in on a spot for a while. My chargers have male banana jacks so I plug in to charge. I must admit you have to pay attention plugging in a battery, you will get a major spark if you attempt crossing (-) and (+).

[Whoaru99]

Do other guys do this? I'm surprised I have not heard of leaving them hooked up together before.

On wilderness trips away from ac charging power, I would just run down one battery and then hook the other one up in it's place. Makes more sense to just leave them them hooked together doesn't it?

IMO, you get more total power from two batteries connected in parallel than using those same two batteries separately but sequentially.

The reason is that the higher AHr load you pull from a battery, the less total AHr can be pulled from the battery. So, when the load is split between two batteries, the AHr load on each is reduced by 1/2, so the total number of AHr that the batteries can give up will be greater.

The total amount of power than can be pulled based on AHr draw is not insignificant. Pulling say 10Ahr from a battery will allow it to give up a meaninfully higher total amount of power than if you draw 20Ahr from that same battery. Just look at the battery mfg capacites at various loads to see how the ratings change.

I posted this information in another example some time ago.

[Wish-I-Were-Fishn]

If I do this, what gauge wire do you recommend?

[BobT]

It depends on your expected maximum load. What will you be using the batteries for?

Bob

[marine_man]

If it's for your trolling motor I'd go with 8 or 10 gauge... preferably 8.

marine_man

[Whoaru99]

Yeah, depends on load and length of wire.

I wouldn't go less than 8 and probably more like 6.

Don't forget the fuse/circuit breaker connected as the first thing off the battery post.

One of the beauties of the 24-volt (or higher) systems is that you can use a smaller gauge of wire to carry the same load. Or, conversely, cut down the voltage drop over the cable.

[Wish-I-Were-Fishn]

I have 6 gage now to the motor with a 50 amp beaker. What gage should I use to connect the two batteries together?

NOTE: read my other posts before you answer this to see what I'm doing

[marine_man]

6, 8 or 10 are just fine in my opinion... especially if the batteries are right next to each other.

marine_man

[Whoaru99]

You could use a smaller gauge since only 1/2 the power will be going though the jumper wires in a parallel circuit. But, I'd probably just stick with the 6ga if you gotta buy some, or use 8ga if you happen to have some layin' around.