Forgot to bring my deep cycle batteries inside for the winter.

Is it really that big a deal? Avg low temps have been mid 20s.

If they were completely charged before the were "left" they should be ok.  If not, it is possible that they could have frozen.  Pull 'em and check them...voltage check, electrolyte (fluid) level.  Put them on a charger for the rest of winter.  Mine are in the our unheated garage but I put them a charger from time to time to keep them up.

check the water levels and give them a charge and take them to auto parts store and have them load tested

On 2016-02-10 at 6:37 AM, Neil McCauley said:

Forgot to bring my deep cycle batteries inside for the winter.

Is it really that big a deal? Avg low temps have been mid 20s.

If they are good batteries and fully charged when you left them they will be fine.  I've stored cars over the winter w/o a single problem.  I always unhook the ground to ensure that there's no draw, even a clock...Did you happen to unhook the ground or at the very least, the TM cable?  Somethings on boat have a fantom draw.

If they were good before, than no. I unhook mine and pull them out of the boat every winter after the final charge after the last trip (making sure they are full of water before they get charged the last time). But they stay out in the cold/unheated storage area all winter. They usually don't see the charger again till 2-3 weeks before the season starts and I have never had any trouble with them. In fact.............the one year I pulled them out and put them in the heated shop at my work over the winter on a trickle charger for several months was the only time I ever had issues out of the gate, and they were not "old" batteries either.