When UPSs go bad

I used to have an apartment at the end of a power-line spur. Outages and interruptions were so frequent that I invested heavily in uninterruptible power supplies for my computers, ISDN modem, etc. Since then I have watched the units fail one by one as their sealed lead-acid batteries wore out. It seems the best one can reasonably expect from a unit's batteries is five years, with two to five years being the range.

Besides the low-battery warnings, there are two interesting hallmarks of failing sealed lead-acid batteries in UPSs. One is the sulfurous odor, probably caused by leaking battery acid or sulfuric acid vapor. Reeks like bad eggs until you unplug the unit and replace the batteries. But a second, very unexpected hallmark that goes hand in hand with the odor is a reading on the carbon monoxide (CO) detector. From a unit in the hall outside the computer room I was getting constant readings of around 10 parts per million (ppm) with a peak at one time of 32 ppm CO before I unplugged the failing UPS. What I'm not sure of is whether the reading was from actual CO or from another vapor that was causing a false positive. I suppose CO is conceivable from the standpoint that sulfuric acid can slowly combust materials is comes in contact with.

So if you ever see your carbon monoxide detector acting up, keep in mind that there's things in your house besides the furnace and stove that can be the cause.