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My Mac is randomly shutting down even though I have an APC UPS. I bought a new Mac, and the same thing is happening with this computer, so it is not a power supply issue. Any ideas?

The UPS battery backup does not go off, indicating any loss of power, and I have to pull the computer plug out and replug it in for it to restart!

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2 Answers 2

It sounds like the battery in your UPS is dead. You can take the whole UPS or just the battery to a local battery outlet like Interstate Batteries and they'll test it for free. Then you can either buy a replacement battery on the spot or directly from APC. (In my experience, it's cheaper and more convenient to buy the battery locally, but you could check APC's price beforehand.)

Typically APC recommends that you replace your battery every 2 years, but I've had batteries fail sooner than that, and I've had several that lasted much longer than that. Although APC recommends against using other brands of batteries, properly-spec'd replacement batteries from other reputable outlets are just as safe to use as APC-brand replacements.

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The simple way to test this is unplug the APC with the computer turned on. If the computer shuts down ( no power ) then the battery is dead, otherwise I could be the computer is overheating, although 2 computers doing the samething is odd. –  Ramhound Mar 19 '12 at 12:28

You should not have to disconnect the load from the UPS to make it work again, therefore i guess a defective UPS. It could also be as easy as the UPS cant provide enough power to the computer and therefore shuts itself down in some kind of overload protection.

When the battery dies in my APC UPS in just beeped all the time and would not supply power. In Linux you can use apcupsd do interface the UPC, the same or equivalent should be possible to do in OS X too.

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