APC BR800 Overload light with beeps

mosfet short

mosfet damaged

mosfet

mosfet

problem is in the inverter

Check 740 mosfets got shorted Repleced then then will be ups ok.

Without knowing which light is flashing I can only guess. From my experience and assuming it is the battery light that is lit and NOT the overload light, it can be one of two things, one is your battery is near the end of its life and needs to be replaced, and the other is that your battery is improperly connected.

To confirm if your battery needs to be replaced or not, you can run a self test. Ensure that the battery has had time to fully charge (and that it is definitely correctly connected), and then turn off the UPS, and turn it back on. It will automatically run a self test.

if the light stays lit, you need to order new batteries. One source is here: http://www.refurbups.com/APC-Back-UPS-RS-900-BR900-Replacement-Batteries

If it IS the overload light that is lit, you simply have too much equipment attached to the UPS, more than the inverter can handle. Try removing some equipment until it turns off.

Internal fault.

UPSs will beep when unplugged to tell you that the mains is off! Overload should reset if you disconnect both the load and the power.

it seems that the inverter circuit of your UPS is dying. the solution here is you have to open up the UPS and check the inverter circuit. to make easier, check the power mosfet if its leaking.