UPS and EPS switchover explained
Many power stations can sit between the wall and your equipment, passing grid power through while keeping their battery charged, then switching to battery when the grid fails. Makers call this UPS mode, EPS, or pass-through with backup. The number that matters is the switchover time.
What the milliseconds mean
When the grid drops, the unit detects the loss and starts its inverter. The gap in between is the switchover time. Equipment with its own power supply rides through a short gap on the energy stored in that supply.
- 10 ms or less: desktop computers, monitors, routers, NAS boxes and most electronics stay on.
- 20 ms: still fine for nearly everything. This is the common spec on good units.
- 30 ms: most electronics are fine; a few sensitive power supplies may reset.
- Above 30 ms, or no rating: treat it as a plain pass-through. Anything plugged in may reboot.
We give feature credit only to units rated at 20 ms or faster.
Why it's not a real UPS
A dedicated uninterruptible power supply of the online or line-interactive type conditions power continuously and has effectively zero switchover. Power stations are standby devices: grid power goes straight through until it fails. For a home office or a media server that is usually acceptable; for medical equipment or lab gear it is not, and the makers say so in the manual.
CPAP machines
A CPAP's bedside power supply tolerates a short gap, and the machine restarts within seconds in any case. The more important numbers for CPAP use are capacity and the DC output: running a CPAP from its DC cord rather than through the inverter avoids the conversion loss and can nearly double runtime. See best power stations for CPAP.
Battery wear in pass-through mode
Leaving a unit plugged in indefinitely keeps the battery near full charge, which ages lithium cells faster than storing them at 50 to 80 percent. Most apps let you set a charge limit; 80 percent is a good standing setting for a unit used mainly as backup.