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An uninterruptible power supply, also called a battery backup, provides power to a computer when the utility mains fails.

UPS usage

A UPS isn’t really completely uninterruptible – it typically only provides power for a few minutes. All main power failures can be divided into two types:

UPS design

Do I want the kind of UPS that I plug power cords down from the top, or in from the back?

What else should I look for in a UPS?

Is it better to design a UPS to recharge the batteries as fast as possible with the mains power comes back on, or to slow charge to give the hydrogen gas more time to dissipate?

Some system administrators recommend the Eaton Powerware and Tripplite UPSes over APC.

For safety reasons, all UPSes must have a way for any hydrogen produced to be safely vented.

UPS battery

Some people are experimenting with running a consumer UPS with a standard, off-the-shelf battery rather than the oddly-sized battery used in many consumer UPSes:

The only "difference between a normal lead-acid car battery and a deep cycle battery" is the design of the lead places. A car batteries has many thin lead plates, perhaps punctured by a few holes in a “lead grid” or many holes in a “lead foam”, while deep cycle batteries have solid thick lead plates. Standard car batteries don’t deal well with deep discharges that a UPS can make.

However, “deep cycle” batteries work great with UPSes.