APC “Battery Disconnected” May Mean Overheating

Mark Berry September 26, 2011

I got an email from APC PowerChute Business Edition that said simply “Battery Disconnected.” The connected UPS is an APC SmartUPS 1500 model DLA1500 (the Dell equivalent of an SUA1500). Of course the battery is not disconnected; the connection inside the unit is a very secure clip that can’t just wiggle loose.

Once I got on site, I found that the “Replace Battery” light was blinking. For some reason there was no corresponding event in the PowerChute event log.

Of greater concern was that the unit was almost too hot to touch. When I got the battery door open, I could see the batteries bulged somewhat and were very hot. The plastic pull tab broke off when I tried to pull out the batteries. I finally managed to hook a wrench around the top and pull them out. And get this:  two hours after removing them, the batteries still felt hot! I guess I’m lucky I didn’t have flammable hydrogen gas escaping as this thread says can happen. I disconnected the two batteries from each other and left them outside overnight to cool.

Reviewing the PowerChute data log, I see that the temperature is usually around 30 Celcius (86 Fahrenheit), but starting at about 7:30am, it slowly climbed to 41 C (106 F). The temperature was 40 C when the unit reported “battery disconnected.” Is it a coincidence that 40 C is the temperature at which the fan turns on (KB article)? Perhaps some safety switch was tripped to disconnect the battery? The fuse between the batteries did not trip.

APC Data Log

Here’s the event log, showing the “battery disconnected” event at 2:39pm:

APC Event Log

And here’s the temperature graphed from 4:10am to 4:50pm:

APC Data Graph

How Hot Is Too Hot?

According to its specs, the DLA1500 is supposed to operate safely in an environment up to 40 C. The building where this unit is installed does not have air conditioning, but the high in San Diego that day was 71 F, so the room was well below 80 F (27 C). I understand that ventilation is important, and I’ll move the UPS to sit on top of the server tower rather than beside it, but clearly the overheating here was not due to a hot room but to a battery or controller failure.

What Should Have Happened

I am definitely concerned that this high-end UPS did not detect a failed battery or an overheating condition earlier. All I got was the “battery disconnected” warning; since the server was still up, I didn’t consider it an emergency. Fortunately, it was a convenient time, so I went on site within a couple hours and discovered the overheated unit.

Next time:  carefully check the Internal UPS Temp column in the Data Log. If it has risen 10 C in one day, consider a shutdown and get on site.

I wondered why PowerChute hadn’t warned me about the overheating. It turns out that the default setting for “UPS Internal Temperature Threshold Exceeded” event is 70 C (158 F):

APC Temp Threshold

Wow! If the unit is almost too hot to touch at 40 C, 70 C seems way too high.

I don’t know how accurate these internal temperature sensors are. At another location, I have an APC SU1400NET that always reports about 40 C, but its case is hardly warm to the touch.

Maybe the solution is to check the normal operating temperature for a given UPS in the Data Log, then to set PowerChute’s UPS Internal Temperature Threshold Exceeded event to trip about 5 degrees above. So if 30 C is normal, set PowerChute to 35 C. Note that this is a full shutdown event by default, but that is certainly preferable to risking a fire in the server room.

Has anyone else seen issues like this? What does PowerChute report as the typical internal temperature of your SmartUPS?

Update November 23, 2013 I just noticed that there is a separate Warning event called UPS Internal Temperature Warning which can be configured to send an email. It makes sense to set that a few degrees lower than the Critical Threshold Exeeded event, which shuts down the machine. That will hopefully give some advance notice of a UPS on its way to overheating.


  1. Neil @ Homepage Computers   |  February 06, 2013 at 6:50 am

    I have recently had the same problem, UPS too hot to touch, battery disconnected warning, batteries overheating, bulged out, terrible smell of hot plastic in the office alerted me when I arrived in the morning.
    I was wondering if you ever tried replacement batteries or found the cause of the problem – I don’t know if I want to trust the unit again or invest in a new battery pack if it is going to be trashed by the UPS.

  2. Mark Berry   |  February 06, 2013 at 9:43 am

    APC replaced that unit under warranty. Apparently the replacement was a refurb since it shows a manufacture date of 2008. I assume the battery was new. No issues since then.

    I did move the unit off the floor (now sits on top of the tower server) and set the UPS Internal Temperature Threshold Exceeded event to shut down at 40 degrees Centigrade instead of 70. Currently it’s running at 22.5 C. The server itself shut down from overheating last summer, and the client installed a small room air conditioner.

    I would definitely call APC. In my opinion, a bulging battery and overheated plastic may indicate a faulty unit, not to mention a fire hazard. A new battery might not solve it. Sometimes companies will replace equipment even past the warranty if there is a real hazard.

  3. Neil @ Homepage Computers   |  February 07, 2013 at 8:40 am

    Hi Mark, really appreciate your prompt response.

    I contacted APC this morning who referred it immediately to 2nd Tier support. They called me a few minutes ago (great service) and are going to replace the battery at their cost (battery was genuine APC 3 yrs old so just at the edge of normal working life). They were confident that the problem is only the battery and the UPS would be safe to use. They were not able to give me any real advice to prevent this in future other than operating the unit in a ‘not-too hot’ environment, approx 20C. There is no way to monitor the battery temp itself with the SUA1500i.

    I will adjust the UPS Internal Temperature Threshold Exceeded event as you suggest.
    I will also monitor the battery temp independently for a while with my digital thermometer to see what happens.

    Thanks again for great advice – that one call to APC saved me £100 as well! Next time I am in San Diego I will buy you a beer!


  4. Mark Berry   |  February 07, 2013 at 9:19 am

    Good to hear, Neil. If that model has a temperature probe, I would think you could see the current temp in the data log (last column of first screen shot above). Use that as a basis for setting the threshold. Also, under Data Log > Configure Log, set Data Log Entry Expiration to something like 1 month so you can go back after an event to see what happened.

  5. Bert Kritzer   |  February 26, 2013 at 7:48 pm

    Slightly similar issue … The “Replace Battery” light came on on my XS 1200 unit.

    I got replacement batteries at Batteries Plus; the guy there assembled the battery pack.

    I put them in the unit, and now the Replace Battery light is flashing. If I look at the unit in Power Chute, it claims there is no battery in the unit.

    I’m thinking that the battery pack was not put together properly, or one of the wires in the joining unit came disconnected.

    I’m inclined to take the battery pack apart and reassemble based on a YouTube video that explains how to do the replacement.

    Any thoughts or experience before I do this, would be helpful.

  6. Mark Berry   |  February 26, 2013 at 9:38 pm

    First I would take the whole thing back to Batteries Plus and get them to double-check it. Have them show you how it’s wired and explain why it’s right. Or if they messed up, hopefully they will make good on it, which they’re unlikely to do if you have been pulling things apart first.

    Failing that, I would test the batteries with a meter, as a pack, then individually. You could also test the voltage output of the UPS. Battery pack assembly for a UPS is not difficult, but it _is_ electricity and if you aren’t familiar with the basics (like, can you confirm you have two 12v batteries in series with a 24v output), or if you don’t have a meter, I’d find a friend to help. Even then, if it was wired wrong and plugged in, I don’t know what that might do to the battery chemistry.

    You could certainly have a faulty UPS; as I said, I had to have mine replaced.

  7. Bert Kritzer   |  February 28, 2013 at 1:40 pm

    Thanks for the quick reply …

    UPDATE: I took the whole unit into Batteries Plus. There was nothing coming out of the plug from the battery, and when they disassembled the pack and tested the batteries, neither was putting out full power. One more of the batteries they pulled from the shelf was iffy, but they came up with two that were good, and now the UPS is working fine.

  8. Mark Berry   |  February 28, 2013 at 1:46 pm

    Bert, glad to hear your Batteries Plus store stood behind its product!

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