Battteries are cells in series. If the battery pack discharges too deeply, then current output by most cells can reverse charge the weakest cell. Sometimes this can result in a short inside that one cell. The entire battery is bad because too much discharging has reverse charged and destroyed one cell. Its rare. But is does happen.
That isn't the issue here. It's the fact that lead-acid cells can be destroyed by a single full discharge.
By the way, I've seen primary alkaline and lithium cells reverse-charged.
The point is that any battery can be harmed by over discharging.
Characteristic of gel cells is that a full discharge left for months means permanent damage. However the OP still must determine if battery has simply failed OR UPS charger circuit is defective. Only then will the first solution be definitive. Makes no sense to buy a new battery only to discover that battery is dead because a UPS charging circuit is defective.
I've never heard of one exploding, I have had them bulge though. Gel cells are certainly prone to sulfation.
They can hold up to a tremendous amount of abuse, but deep discharging will kill them just about every time.
No, the point is that lead-acid cells are especially susceptible to being damaged. I've never had this happen with a nickel-cadmium battery.
The point: identify the reason for a failed battery (defective battery or defective charger circuit) before replacing that battery. The point is to answer the OPs question with a useful diagnostic procedure.
Secondary is a claim that only gel cells get destroyed by discharging. Any battery can be damaged by excessive discharging. Which is not relevant to the OP's problem since he apparently has a dead battery. Primary point is why. A question that is answered in seconds before buying expensive replacement parts. Makes no sense replacing a battery if the charger circuit was defective (created a dead battery). A question that can be answered in seconds.
And the result is ...
They wouldn't even start to take a charge. My trickle charge reported both were fully charged, even though they were totally dead. Even a couple of hours on each wouldn't make them budge.
So, time for some new batteries. The originals were made in China. Will hopefully remember to post whether the new batteries fixed the unit.
-Brian
P.S. There are four small-matchbox size black boxes on the unit's PCB. I think they are relays. My guess would be that the batteries must have some juice to keep one of these relays closed -- and that relay admits line voltage to the entire device. Would explain the total non-response from the UPS when plugged in with dead batteries.
You can hook up just about any lead-acid battery of the correct voltage for testing, should be fine to jumper it to your car battery to see if it powers up, mind the polarity though.
I put a pair of 'cheap' batteries in my APC 700 when the originals failed. They lasted all of a few months before it kept falling over again when it performed its auto self test every couple of weeks. Kept doing it in the middle of the night so we thought it was a smoke alarm going off. A new pair of 'proper' priced ones restored it. Also, be very careful that you get replacements with the right sized spades. Before fitting the cheapies, I had already tried a pair of batteries with similar size and capacity, but small tags. These were in good condition and still give good heavy duty service now in another application. However, with the large connectors in the APC
700, pushed onto the small tags on the batteries, there was just not enough contact area, and it fell over every time at powerup, when it does its load test, and checks for battery terminal voltage drop.Arfa
No reason to remove or disconnect those batteries. Simply connect a VDC multimeter to battery terminals. If voltage rises when UPS is connected to AC, then UPS charger is working. Same charger test performed without removing anything also tests other UPS hardware. Procedure tests both items simultaneously. Learn more, faster, by also doing less labor. Use a meter.
But it's just been explained that one of the relays is in series with the AC input line, and doesn't close unless there is at least some residual charge on the batteries. Therefore, it would seem that there is every need to disconnect and at least sub those batteries, before being able to carry out any kind of charging test. I would further suggest that a simple charge voltage test, may not give an accurate picture of what is actually happening in the charging circuit. Even a charge current test, although a better indication, may not be sufficient, unless you know what the charge limit current should be, either for all or specific battery discharge conditions. FWIW, I can also confirm that an APC 700 model will not even try to start up without a partially charged battery fitted.
Arfa
I used two car batteris to power my UPS during a hurricane here a few years ago.
Note: Some SmartUPS units require 24 volts.. i.e. 2 12v batteries in series to run.
Mike
Yes, this unit has two 12V batteries. New ones are on order! Shipping is more than the batteries themselves ... they are heavy.
-Brian
Did you check locally? Many places carry a selection, Frys had a whole shelf of them, I don't recall what the prices were like though.
Batteries Plus with many retail locations sell them for a fair price as well.
Bob
Try BatteryPlex.com.
I buy through local alarm companies. Call two or three and at least one will sell over the counter.
-- Barack Obama, May 9: "I\'ve now been in 57 states? I think one left to go."
Just got 'em (via eBay) -- "Rhino" brand; about US$16 each, including shipping. Look good, and hopefully will work well! Best retail price I saw, plus shipping, was about $32 each.
-Brian
I'll check next time. My last set was local and in between those prices.
-- Barack Obama, May 9: "I\'ve now been in 57 states? I think one left to go."
Good! There's only one batteries-only dealer here in town, and it is about a 15 mile round trip. So add ~$3 for gas ...
Installed the new batteries yesterday. As warned, the lugs were smaller, so I had to crimp-down one connector slightly to get a tighter fit.
Also, the last connection was shocking! Actually sparking -- one huge bolt, and I'm glad I wasn't in its way. There's a good-sized capacitor internally to the UPS, and my guess is that the batteries needed to recharge it upon connection.
The UPS then worked normally! So yes, as the early responders answered, it was simply dead batteries. Will recycle the old ones, and keep the UPS plugged-in continuously so that hopefully these new batteries will last a long time.
-Brian
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