BE750G (Back-UPS ES 750) no longer fully charging battery, low charging voltage

[Anonymous user]

I have two BE750G UPS units manufactured in Jan 2008.  Both had new batteries installed in July 2014 (originals had little capacity remaining), and now both are failing to charge properly.  Batteries were exact replacement for original. 

First indication of a problem was that the BE750G on my main computer was showing only 75% to 85% charged, never full.  First I suspected bad battery, but the battery checked OK on a dedicated 2A charger and would charge to above 12.6V (measured with open circuit).   With battery installed in the BE750G and charging, terminal voltage was only about 12.4V.  Even with a completely full battery charged to 100% on different UPS model, the terminal voltage after installing into BE750G would droop to 12.4V by next morning.  I know from SLA battery experience and experiments on other APC UPS units that float charge voltage should be 13.5V.  I swapped around several batteries from other similar UPS, and put the battery where I originally noticed the problem into another good UPS, and it charged to 100% with 13.5V float as expected.  Problems tracked with the BE750G UPS, not with the batteries. 

I checked the second BE750G unit, and it too was no longer charging to 100% full.  Its float voltage was slightly higher at 12.6V and indicated via USB a charge level of 93% or slightly higher, but not 100% (using Win 7 Pro HID battery driver to monitor). 

So both these BE750G units no longer seem to be able to fully charge a good battery.  Anyone have a suggestion for cause of this type of failure, and if repair is possible?   I have capability to replace any part on the circuit board, but I don't have a schematic to start debug and the circuitry looks too complex to reverse engineer in any reasonable time.  If an APC tech could tell me where to look, I could probe any voltages or waveforms.

I'd hate to have to replace both these units when they already have new batteries and inverter still works fine.  This BE750G model is still available for sale and I don't even need 500 wattage system anymore, but if the electronics only have a 6 year life span, I honestly can't purchase another of same model.  Really I need about a 300W unit with largest battery and runtime available. 

Thanks in advance for any advice. 

[Anonymous user · Accepted solution]

Same issue at my place...Were you able to resolve this? Thanks.

[Anonymous user]

Same issue for me.  Any solution? Thanks.