Battery tender & storage

Several things to consider, some maintenance chargers will drain your batteries if the power goes off. I found this out the hard way after a lightning storm knock out the power to my house. Secondly cold temperatures greatly reduce the self-discharge, heat increases it. What is the temperature that the batteries will see during storage? Some data points. My house batteries on the MH were charged in Oct and checked in March and were still at 80% SOC. The switch was just turned off cables not disconnected. Those batteries are 15 years old. My Chassis battery was at 90% SOC and I disconnected the neg cable. That battery is 3 years old. I just got my boat out of storage yesterday after 7 months of storage and the negative cable removed, that battery only one year old read 12.5 v. I never recharged it before I used it yesterday to go out fishing. I believe keeping your batteries plugged in 24/7 eats your plates away quicker than leaving your MH unplugged and recharging when the SOC reaches 80-90%.