Our UPS is hooked up to three Exide Powersafe EP65-12 SLA (Sealed Lead Acid) batteries. Normally, that gives us about six hours of backup time for my desktop, monitor, and a few assorted peripherals. It's not often that the mains power is off for so long (less than half a dozen times a year, I'd guess), but that capacity has proven invaluable in the past. For the last few months, however, the UPS has lasted for half an hour at most, even when the batteries were fully charged. Using a multimeter, I found that the voltage across one of the batteries fell rapidly to 10.5V just before the UPS died, while the other two remained above 12V. Since the batteries were still under warranty, I contacted the vendor to ask about having them replaced (which I have had to do in the past)
Unlike last time, the vendor told me to register a complaint with Exide, which I did after some delay due to external circumstances. An engineer was dispatched to visit me a couple of days later, and after testing the system, he agreed with my diagnosis: one battery was bad. He wrote up a report and went on his way after telling me that the replacement should arrive in a few days. Unfortunately, what did arrive the next day was email from his supervisor, saying they couldn't replace the battery because the charging current was "too low". (The mail also said that I didn't have the original invoice for the purchase of the batteries, but that was just the engineer trying to cover his ass after forgetting to ask me for it.)
I was surprised, to say the least, because the engineer had given me no reason to think there was any problem during his visit. I called my UPS vendor (Compact UPS) to discuss the problem. They had serviced the UPS a few months earlier, and assured me that nothing was wrong with it. They told me that they restricted the charging current to slightly less than 6.5A—which is the minimum that Mr. Gupta said was needed—because they had experienced problems in the past with charging Exide batteries at a higher current. Armed with this knowledge, I arranged for a joint visit with both Exide and Compact UPS engineers early the next week.
The UPS guy arrived first, and tested the system. The Exide guy arrived half an hour later, and repeated the tests. Both agreed that the battery was undoubtedly bad, and neither thought the problem had anything to do with the charging current. (We also observed that when the mains power was switched on, the current started out at over 5A and dropped very quickly to 3.7A as the battery's voltage came up, making the UPS think it was fully charged.) The UPS guy explained his take on the current question to the Exide guy, who offered no disagreement. Both said they were surprised that the battery had lasted even as long as it had.
But this was not good enough to change Exide's mind about honouring the warranty. Mr. Gupta again refused to replace the battery, even though the charging current was obviously dropping when observed because the batteries appeared to be fully charged; and even though the other two batteries worked fine, which seems rather unlikely if the charger were somehow broken; and even though both of his own engineers thought the battery was at fault independent of the charging current. I replied to him to make these points, and he replied to say that my battery "worked perfectly for a period of more than 10 months" (which exaggerates the truth by a few months, but the delay in reporting the problem was my fault entirely, not his), and that the warranty applies only if the battery was maintained according to the conditions specified in the warranty card, which did not cover "improper charging".
I fished the warranty card out from my records and looked at it. It does
exclude problems caused by "improper charging", but the parameters given
specify only a maximum current of 0.2CA (i.e. 13A), no minimum.
Furthermore, nobody has offered a credible explanation for how charging
at a marginally lower current could have damaged only one battery out of
three. (Remember: the batteries were nowhere near fully drained in these
tests, so when the mains power was switched on, their voltage was higher
than it would have been if they were drained, and so the charger applied
a smaller current; Ohm's law.) The
also recommends a lower charging current:
The exception is not to
use a charger (or charging setting) for SLA batteries that is greater
than 10% of the AH (C/20) capacity.
Of course, it's in Exide's interest to claim "improper charging" and deny warranty claims, especially close to the end of the one-year warranty period. I'm afraid this means I will no longer buy or recommend Exide batteries again (especially after both the UPS engineer and the Exide engineer gave me the distinct impression that it was increasingly common for Exide to try to deny legitimate claims these days).
Rocket (formerly Global Yuasa) batteries seem like a credible replacement.
Update (2012-11-29): I filed a case against Exide at the District Consumer Forum ("consumer court") in August 2010. After nearly two and a half years of monthly hearings and interminable delays caused by Exide, I have received a judgement in my favour.
Exide was ordered to replace the faulty battery and compensate me for court costs and the harassment I was subjected to (in the view of the court).
Update (2013-01-08): Exide replaced all three batteries and sent me a cheque for the compensation amount.