Question about batteries in series

[plasticmaster]

I have a 24V trolling motor on my boat powered by 2 - 12V batteries in series. One of the batteries is dead and needs replacing. Can I replace the dead battery with one that has a higher Amp-Hour rating? The other good battery is 550 Amp-hour and I?m thinking about putting a 700 Amp-hour battery in series with it since the price of them is within a few dollars of each other. Is it OK to have these in series? They are both 12V, but one would be 550 Amp-hour and the other 700 Amp-hour. Thanks.

 

[Fl_Richard]

Re: Question about batteries in series

Sure . But remember one the lower ah battery will go dead first and draw down the higher amp hour battery. My guess is when the batteries are going dead the troller will lumber along longer than two matched batteries which die at the same time.

 

[simplystressed]

Re: Question about batteries in series

Sure . But remember one the lower ah battery will go dead first and draw down the higher amp hour battery. My guess is when the batteries are going dead the troller will lumber along longer than two matched batteries which die at the same time.

This will ruin the smaller battery as it'll drain it right to 0 won't it? As the 24V motor will keep running on both? Someone please clarify

 

[Silvertip]

Re: Question about batteries in series

It is a moot point. If you regularly run a trolling so long that you actually kill the battery(ies), it doesn't matter which one dies first. That action will likely send both of them to battery heaven.

 

[simplystressed]

Re: Question about batteries in series

It is a moot point. If you regularly run a trolling so long that you actually kill the battery(ies), it doesn't matter which one dies first. That action will likely send both of them to battery heaven.

I'm more saying if I have a 55AH battery and a 100AH battery. I assume the 55AH will battery will die and motor will stop working? So you should have the same size battery?

 

[Silvertip]

Re: Question about batteries in series

For optimum performance in a 24 volt system I agree that both batteries shoujld be the same capacity and type. But because one battery dies the motor doesn't actually stop working. It will run very slowing, making more heat than power and in the process sucking the other battery dry and not doing the motor any good either. Next time you replace batteries in your multi-cell flashlight, as the light just begins to dim, measure the voltage of each cell. You will find that at least one is higher than the rest. That cell(s) provides enough juice to light the bulb, although very dim, for a period of time and then it too goes dead.

 

[Fl_Richard]

Re: Question about batteries in series

The lower battery wont go to zero, it will become depleted and draw a "charge" from the larger battery thus dropping the output of the larger battery quicker.

Regardless, if you run your troller until the batteries are dead it's not good for the batteries. If you've never killed the trolling batteries then you'l' probably be just fine. Next time you replace the batteries buy them to match.

Have fun go fishing and dont kill your batteries!