APC UPS es 500 keeps on beeping after 5 sec after it has been turned on. I check the output voltage-ok, I dismounted the 12 V battery from the ups and tested it by a multitester and it reads up to 12 V....what should I do next?

SOURCE: APC UPS no power

The unit might have a dead battery, blow fuse, or a bad board.
Your best bet is to talk to an APC rep. Worst case, APC has a trade in program, and can give you a discount on a new one.
Good luck.

Try Chatting with an APC Support agent online.
Here is their direct link:
http://www.apc.com/support/chat.cfm
Chat with a Support Agent
Chat with Support for immediate assistance with your APC Back-UPS, Cable, Surge Protection, Notebook and Mobile Device accessories and products. Agents are available Monday through Friday from 8:00 a.m. to 8:00 p.m.

SOURCE: UPS Switching off while working

Hi kumaraswamy5,
it seems that either the UPS is connected to an outled which isn't grounded properly or the battery inside of the UPS needs a replacement.
On APC's website you can find the compatible batteries for your device and where to order them. Replacing the batteries is very easy so don't be afraid of that!
Greetings from Germany,
noris017
PS: Please don't forget to rate this advice after you've tested it out! Thanks in advance and have a nice day!

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: i want to connect an automotive external battery

you can get an old ups with bad batt. cheap,take out bad batt,hook yours in,or get a small battery charger(2/10 amp),an inverter(about a 1000watt),plug in charger, hook to batt.,then connect inverter to batt,plug computer into inverter,turn on inverter and you should be good, keep in mind all inverters are not same,get one at a computer store that will handle what your computer draws(watts), if your ups is good and you're trying to expand batt. capacity, the batts. in the ups are not lead/acid,so it's not a good idea to connect different types and sizes or an old batt. to new one,chargers are different too,what I described at top is basically a ups

SOURCE: red light and beeping

change the battery