Solar Panel Wattage Size Needed To Keep Trailer Batteries Charged While In Winter Storage

Question:

I have 2 12 volt deep cel batteries in my Vanleigh vilano how big of a solar system to maintain my batteries after I wi terize so that I dont have to take the batteries out.

asked by: Larry R

Expert Reply:

A lead acid battery will typically discharge anywhere from 3% to 20% in a month's time and will typically have a higher discharge rate during cold weather. The wattage size needed to keep your batteries charged will depend on how large of an amp hour bank you have with the two batteries and how much sun light the panel is actually receiving.

If your two batteries were rated for 100 amp hours for a total of 200 amp hours and you had such a cold winter that you were at a 20% discharge rate that would equal about 50amps in a months time, or about 1.66amps per day. The OptiMate Solar Duo Solar Charging System # MA79JR you were looking at has a 1.67amp charge rate per hour (in peak conditions) so you should realistically be able to charge the battery bank quicker than it can discharge.

Obviously there can be days where you get little to no sunlight or your battery bank could have a larger amp hour rating so you'll want to consider this before purchasing the # MA79JR. You could play it safe and go a little bigger with the 40 watt # MA29JR (3.33amps) or 60 watt # MA36JR (5 amps) if you wanted to.

expert reply by: Kevin C