I’ve often thought about adding a large AGM battery (or three) to the shack to provide for power in the event that all else fails. And then a few days ago I happened across this message from Dave, K9DC about the Progressive Dynamics PD9270 70 ampere power supply.
Basically it’s a filtered, regulated, 13.6V power supply capable of 70 amps continuous. It automatically scans 13.2, 13.6 and 14.4 volts and determines if there is a battery present. If there is, it starts out at 14.4V (boost mode) until the battery is 90% charged, then drops to 13.6V (standard) for 30 hours, then drops to 13.2V (float mode). While in float mode, every 20 hours, it switches to 14.4v for 15 minutes. This prevents battery sulfating, without overcharging. If there is no battery, it simply stays at 13.6 volts.
Because of the automatic voltage switching, you can charge nearly any battery you have for standby power. At my UHF site, I have a 100AmpHour and a 55 AmpHour AGM battery simply connected in parallel. This gives me several hours of full power operation of the repeater. At the VHF site, where I have an automatic backup generator, just a single 55AH AGM battery is present.
Progressive Dynamics sells these power supplies primarily into the RV and marine industries. Cost is roughly $220 from Amazon (compare to a 70 amp Astron for ~$475).