ES 750 UPS -- battery seems OK but outlets do not function on battery power

[Anonymous user]

I'm pretty sure that my ES 750 is over 3 years old, but I didn't put it to use right away after I got it.  It has been running for perhaps 2.5 years straight.  When plugged into a live wall outlet, all of the outlets on the ES 750 are functioning.  But when power is cut, the ES 750 outlets don't provide any power.  The Master Enable light is on.  The Power light is on.  And without power, about 4 times every 30 seconds the ES 750 will beep (and power light goes out during beeping).

I pulled the battery and used a multi-meter to check it.  It is showing 13 volts.  The battery seems to be fine.

Note that this ES 750 UPS sits under my desk with fairly adequate ventilation.  It has not been abused or anything.

What could be wrong?  Is what I have described a known issue that can happen?

[Anonymous user]

I have heard reports of these and similar models failing with no power to the outlets (on either utility or battery power). I have yet to come across one that is broken in that way.

It's possible that the battery is worn out, but I'm not comfortable enough with that idea to conclusively say it is the problem. Extended storage (more than about six months) will shorten battery lifetime. Were the battery actually bad, I wouldn't expect the unit to behave normally when line power is disconnected. It should either produce a continuous beep to indicate a depleted battery or fall flat on its face and shut down immediately.

You might have to place some kind of load on the battery for your voltage test to be meaningful.

The serial number can tell you when your unit was manufactured. Skip over the first two digits or letters, and the next four numbers will indicate the year and week of manufacture.

[Anonymous user]

Thanks, William.  I get you on the battery load, how batteries can sometimes show full voltage but be worn in such a way as to not handle a load.  I tested it very simply with charging my cellphone, which is a low draw... and I got nothing from it.

My serial number is 3B0930X19110.  So I presume 2009 and week 30.  I had it mothballed for a bit longer than I remembered (it was the situation of buying it, stowing it away with the intention of installing, but then I moved and completely forgot about it until unpacked about 3~4 years ago).  Perhaps the battery is too old.  Looking at the cost of replacement batteries, I'm thinking it's probably best to just go with a newer unit, given the hardware and firmware improvements.  Would you agree?

[Anonymous user · Accepted solution]

You are correct regarding the unit's date of manufacture. The battery in these units lasts between three and five years. Extended storage shortens battery lifetime further.

Generic replacement batteries are available for these units at lower cost than a genuine APC replacement battery. If you want a new unit and buy direct from APC, a trade-in program is available in many countries that will ensure your old UPS is properly recycled while giving you a bit of a discount on a new one.

If there is any question about the unit's performance or functionality, it probably would be best to replace it with a new unit. (I can't say to what extent the firmware in newer units has been changed, since I'm just an end user. I have repaired some of these in the past, and haven't seen a whole lot of change in the circuit design on these more basic models.)