Battery charge (capacity) indicator on Back-UPS XS 1300

[Anonymous user]

I have two or three of these units in my systems. It seems that the battery charge indicators are way off when indicating battery health. I had a recent incident where there battery capacity indicator showed 5 bars (full capacity) when the unit started beeping. It was online with full AC line voltage. After a few minutes the display went black (off) and the unit shutdown. No bad battery indicator was displayed. I pulled the unit and checked the voltage on the 12V batteries, and they were down to 3V! No way these should have indicated full power. What is wrong with these products?

After replacing the batteries the unit is now working normally. So its not a malfunction that I can determine as the unit does fire up and run normally.

I ran another test where I pulled the batteries from another XS 1300 that were reading full charge. After re-install (10-15 min later) the very same batteries read 2 bars. Now how can that be? They did not loose over half their charge in 15 min. I am beginning to think that the battery capacity indicator is totally worthless. If this indicator is simply the voltage of the batteries then it makes sense, BUT THAT IS NO INDICATOR OF CAPACITY, because even a dead battery will read 14.5 V if it has a charger connected due to high internal impedance.

Given this, how can a user really tell how much life is left in their batteries? I would like to proactively plan for replacements before they go fubar and you are left scrambling for replacements.

[Anonymous user]

If the batteries in these units are left on float charge for a long enough time, they can be damaged by overcharging. This won't be detected by the battery monitoring unless it happens during a self-test. (The higher end Smart-UPS models conduct such a test every two weeks. I don't think any of the Back-UPS models behave similarly unless connected to a computer and used with Powerchute or other software that can command a self-test on a schedule, if a given UPS supports such capability. Not all of the Back-UPS line supports a self test under software control.)

Even in the models that do a scheduled self test, the load can still be unexpectedly dropped or restarted if the batteries are bad enough.

This failure by overcharging may very well be what has happened to the batteries in your unit. Batteries with swollen or broken cases have usually fallen victim to overcharging damage.

If you want to be proactive, I'd recommend replacing the batteries no more than every two or three years, depending upon power quality. Then you can be sure that they will be functional when needed.

This is a common problem with any UPS regardless of its maker.

[Anonymous user · Accepted solution]

William

Thanks for your reply.

First, a product as expensive as a XS 1300 should never overcharge lead acid batteries, no matter how long the system remains powered up. I have float chargers for my car batteries that are smart enough not overcharge a battery so this is not rocket science technology. If the unit is overcharging batteries then it is defective in operation or by design. My batteries showed no sign of swelling. An open circuit voltage of 3V indicated these were completely gone. That battery capacity indicator should not have indicated full charge. I can understand this occurring after a power failure where the batteries were discharging at a high rate, but no such stress was applied to these batteries. They were on standby for 99% of two years. No way a properly set up maintenance charger should have killed these in that time period.

Second, if the battery capacity indicator is just another voltage measurement, then APC should say so and not advertise it as a battery capacity measurement.

I suspect the real problem may be that the UPS is undercharging rather than overcharging. AGM batteries need to be charged with a specific charging profile to maintain close to 100% capacity. If they are undercharged they can loose 30, 40% or more in capacity. Many trickle charging strategies do not provide enough current to maintain these batteries. I use Odyssey AGM batteries in my car and they need special chargers. But if charged correctly, they last for 5 to 8 years, way more than any UPS battery has lasted in an APC UPS.