Using two 12V batteries in series with both a 12V and 24V output Answered
I have a tornado shelter
that I have wired for both 120V AC and 12V DC. All of the lighting is via 12V DC while the AC is used for recharging the batteries and running a 1500 VA UPS system that powers a small TV and radio. The UPS system normally uses two small 12V SLA batteries in series. To increase the run time of the UPS I want to use auto batteries instead of the small SLA batteries normally used. In order to cut down on the cost of batteries I want to use two auto batteries, one 100AH battery used for the main lighting and a 50AH battery in series with the 100AH battery to provide the 24 volts for the UPS system. The UPS system will only use the two batteries when the AC is out which is normally rare. Do you see any problems with this setup providing I install a diode in the UPS battery feed to prevent the UPS from recharging the batteries and use separate smart chargers connected to each individual battery? I feel I have overlooked something but I can't seem to put my finger on it.