If you have a UPS kicking around you can hack it to be used for all of your low voltage applications. The UPS has a battery and charging circuit in a nice case, by hacking out the inverter you can reduce the load when the power fails. Now of course you won’t have 110VAC available but these days there are so many things that need 12 volts. A handy side mounted battery voltage monitor lets you check to see what your battery voltage is so you don’t drain it too low. Plug in USB converters are used but I would have liked to see some switched ones that were fixed onto the case somewhere for convenience.