I use TWO different backup batteries.
1. 12V 25Ah Gates Cyclon Rechargeable.
2. 12V 38Ah Panasonic Gel-Cell.

The 25Ah battery is connected to a 20Amp
Astron via a 25A reverse current protection diode.

The 38Ah battery is connected to a 35Amp
Astron via a 45A reverse current protection diode.

Each of the Astron's voltage was adjusted to provide
to float the batteries @ about 13.6V.

Each combo runs various 12V stuff in the shack.
When the power goes off, I don't notice it!

The 25Ah battery has been in continuous service
for almost 10 years and still delivers about 85% of
it's capacity. - YMMV!!