Today only woot has this ups for the best price I've seen it.
Price includes a today-only extra 10% off for prime members. To get the discount to show up you need the following:
1. Use the woot app.
2. Sign into app using your Amazon prime account (not woot account)
3. In checkout, verify your address
After these 3 things the extra discount should show.
This is refurbished, but the notes say that the batteries have been replaced.
Seems like a pretty good deal for a simulated sine wave 810w ups.