I store my FR 3051S inside of a barn with power available. I generally donít have battery problems but this year due to Covid-19 the unit has set longer than usual and all 3 batteries went dead. The engine battery and 1 house lived after charging. To prevent this problem, because it may not be used this year, I bought a battery tender. I am looking for thoughts to protect all 3 batteries. My thought is use shore power to maintain the house batteries then plug a battery tender into the house to maintain the engine battery. Any better ideas and will this be a good idea letting it sit like this until spring??