The last time we bought one of these it was only around $85 and it's
a din rail mount with a side din rail battery mounted connected via a
module cable. The battery isn't inside the unit. If the battery goes
bad, it will shut down. the inverter does not use source supply to power
its output.

Please provide name & model of this stellar, inexpensive UPS. After
determining the cause of our power problems it might come in handy.

Sparky