I've got about half a dozen SLR customer repeaters and all of them are equipped with battery backup. I use inexpensive 100Ah marine grade sealed lead-acid battery, and an external Victron 13Amp fully automatic 3-stage charger, with the internal charger from the SLR disabled. It would take way too long for the limited internal charger alone to get the battery anywhere near fully charged in a reasonable amount of time, hence the external charger addition.
Given the SLR takes about 10amps at full (55W) tx power, battery can last anywhere between 12-24 hours, depending on repeater activity. Most sites also have generator backup, so battery usually only has to carry over until it kicks in, but at times also saved the day when the generator would for some reason not start.
One idea to extend battery operating time was to have a relay coil connected to the AC mains, and a normally open contact connected to one of the GPIO pins on the rear of the SLR and set it to switch to channel 2, then program ch1 as regular full power service, and ch2 for 25w or whatever lower power the system can get away with, and extend battery life with less current demand. But so far have not implemented that yet, but it should be a perfectly viable option.
