For no apparent reason the APC makes a tone and the battery light comes on as tho power is lost, but the power is fine, have checked the plug in in the wall its tight. Un plugged the unit and back in again and after 30 min it occured again. The battery was replaced in the APC last year with no power losses since. Have by passed the APC for now but would like to fix it.

SOURCE: APC Back-UPS ES 500: green light flashes&continuous warning tone

On this unit, the likely culprit is the battery and that it needs to be replaced.

With that, you may want to think about the pros and cons of replacement versus buying an entirely new unit.

This unit is a relatively low end ups and the surge supression uses MOVs that wear out with repeated absorption of energetic spikes. That's why the better (and higher cost) UPSs and surge suppressors don't use them. They're not really that good anyway due to their relatively high transient impedance. The better equipment uses a "transorb" -- basically a back-to-back high voltage zener diode optimized for low breakover impedance and high instantaneous power capability. Unless the transient exceeds the design parameters of the circuit, these do not wear out and do not degrade. That being said, I will assume that you would likely replace this unit with a similar one.
The flashing may not be the battery at all and may be the charging circuitry, thus your new battery may not live very long (half the life that you would expect.

Many batteries out there are refurbs and have issues as all used parts do.

If you contact APC, they will likely give you a 35% discount on purchasing a new product.

The difference in price in the battery replacement vs. ups replacement at this level may only be a few dollars more.

I promise that I am not a UPS salesman, I just deal with many on a daily basis; therefore I am giving my two cents to try to thelp you avoid problems a year from now.

Testimonial: "Outstanding answer with right amount of detail. I swapped battery with identical APC UPS that I have and vfd that battery was cause of warning tone."

SOURCE: apc ups flashes red light to replace battery, but battery is new

i think by replacing the battery has not been the solution to the problem

u need to check the battery charging voltage when turned ON with main electricity, if no voltage present from charger, there is no question of battery getting charged and also once the battery is down with charge it may not re charge hence the indicator and alarm.
recomended to nearest service centre

SOURCE: APC Smart-UPS RT 1000VA

Hello Dear Specialists I have a problem with the APC Smart-UPS smart 1000VA: when I insert the
power plug in the wall outlet in one ups , indicate the AVR Boost ups regulating low AC voltage, when I measuring the AC city power voltage that is 207v .whey this ups is not working about the AC low voltage? ,but it should be work from (170v ~ 230v) AC input volte.please solve this problem, which element of AVR from the ups is failed or wrong and give me free circuit diagram low & high AVR and charger and inverter circuits. thanks allot

SOURCE: APC Smart UPS 3000VA - Dead UPS

ok how long you brought the ups and how long you had not start the the ups usaully ups is power dead change the battery and try to power up it should work be sure that all connection is connect properly before power up the ups.. if the ups doest work that will be the mainboard problem you hav to call for vedor to repair the unit.. yes these fuse for the ups but it unlikely to be blown so should worry of the fuse it self.. change of battery come with different spefc for the ups.. eg su3000rmi3u, sua3000rmi3u, su3000rmxl3u --- battery replacement is 8 pcs of 12v 7ah. sua3000rmi2u-- 6 pcs of 12v 7ah or 8 pcs 12v 5ah. su3000rminet-- 4 pcs 12v 17ah,

SOURCE: apc xs 1500 overloads even with nothing plugged

Hi,

Plz check MOSFET which working in inverter section.