Realistically, how much charge will I lose if i have fully charged batteries and leave them unplugged overnight in, say, 32 degrees temps with the expectation of fishing the next morning? 

Assuming the batteries are in decent shape, not enough to even worry about.

Thanks. I didn’t think so, but wanted 2nd or 50th opinion. 

Almost nothing.  Less in cold temperature than if it was warm.

My estimation is you will lose between 9 and 28 seconds of trolling motor power the next day,  depending on the wind. ?

 

The self discharge rate is typically about 5% a month but can vary a lot depending on many factors.

2 hours ago, Reel said:

Less in cold temperature than if it was warm.

Huh?  Batteries discharge quicker in cold temps than in warm temps.  At least mine do.

Discharge faster in cold than warm. But no you won’t have any issues with fully charged battery overnight in 32* temp. If you do you have battery issues.

32 degrees is not cold.  Check if you want.  At that temperature the batteries hold their charge longer than at say 90 degrees.

19 hours ago, gimruis said:

Huh?  Batteries discharge quicker in cold temps than in warm temps.  At least mine do.

They technically discharge quicker in warm temperatures than cold.  But they're less efficient and can't put out as many amps in cold temperatures (hence why they discharge slower).  So you're more likely to have "dead" battery issues in cold weather, even if technically the battery has more charge left in it.  

17 hours ago, Reel said:

32 degrees is not cold.  Check if you want. 

Check if 32 degrees is "cold?"  I don't even know what that means.  From a raw physics stand point, 32 degrees F is the freezing point.

 

I guess is all relative.  32 degrees is pretty warm here for January.  But in June, 32 degrees is really cold.

3 hours ago, gimruis said:

Check if 32 degrees is "cold?"  I don't even know what that means.  From a raw physics stand point, 32 degrees F is the freezing point.

 

I guess is all relative.  32 degrees is pretty warm here for January.  But in June, 32 degrees is really cold.

Heck.. I thought 32* for you minnasnowdons was early summer temps.. ??