Originally Posted By: dougwalkabout


It has an internal sealed lead-acid (SLA) battery and a pure sine wave inverter. .....

I've tried restarting by plugging them into a modified sine wave inverter with no luck; maybe I need to attach an earth ground.


Unless you get the more expensive UPS systems, most of the ones for home computers are modified sine. You can't plug them into another modified sine wave UPS, because it sees an irregular waverform and automatically switches to battery, which is what it's supposed to do.