Battery Backed external power supply

We have a small unit which has a external power supply of 7V. This unit
draws around 100mA. We have been asked to supply some sort of battery
backup for it. There is no ups to hand so what we are looking for is a
DC small DC supply 7 to 15V which can power the unit from the mains and
keep powering the unit for around 2 hours on power fail. This could be
a external battery that connects in line between the current power
supply and the unit, or a totally new power supply with integrated
battery. The batterys will need to be accessable to allow them to be
changed once a year. I know I could design and build something but
wondered if there is anything on the market. We would want several
hundred of these. Any advice/help would be appreciated.

Thanks

.

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