ATT Microcell in Austin, TX

[list at satchell.net (Stephen Satchell)]

There is power backup and then there is power backup.

The former is a small power pack (batteries, supercapacitors, whatever) 
that will allow the microcell to weather a short blackout or brownout. 
We are talking seconds, to bridge switching transits.  To be useful in a 
deployment, such a holdover battery needs to be very low maintenance. 
(Think about cars that use supercapacitors as a battery replacement -- 
good for short needs like a single engine start.)

The latter is longer-life power to keep the microcell going for days or 
weeks.  It's debatable whether this is mandatory.