TL;DR How should a set of 4 lead acid batteries (12 V, 9AH) be connected for an APC SmartUPS model SURTA 2000 XL?

This afternoon I set about to replace the batteries on our server room UPS, a job I have done before. We ordered the same batteries we have ordered before (last time was about 2-3 years ago). I removed the battery cartridge & opened it, then I methodically replaced each battery in turn - first removing the old one and replacing it with a new one, taking care to connect it the same way (or so I thought).

Unfortunately, when I connected the battery cartridge to the unit, it immediately shut down. After scrambling to restart the servers which had just been unceremoniously powered off, I removed the cartridge again and double-checked the connections, making sure each was firmly connected, and reconnected the cartridge. This time, the UPS came on (without pressing the power button), but it only stayed on for 3-4 seconds before shutting down briefly and coming on again, and cycling through these state (on for 3-4 seconds, shutting off, then coming on again for 3-4 seconds).

The obvious conclusion is that I connected the batteries incorrectly, but I was very careful to copy the configuration I found. And if that's the case, I must admit I'm at a loss as to how to connect them correctly.

Here's a quick sketch of the way the batteries were connected: UPS Battery Configuration

The connection to the UPS is in the upper-right hand corner. The batteries were connected red to red and black to black, except for one white connector between the black terminal on battery 2 and the red terminal on battery 1. This struck me as odd when I first opened the cartridge, but I went ahead & copied the configuration I found.

I'll admit that my understanding of batteries & electricity is limited. I've searched for a diagram of the correct battery configuration, but I can't find one (or perhaps I'm not searching for the correct terms).

Is this arrangement of batteries correct? And if it's not correct, how should they be connected?

  • 2
    \$\begingroup\$ I would go to the vendor site, find the support link and download the manual for the specific device. I imagine you will find the battery connection information detailed in this document. As it stands the connections do not make sense, the connections on battery 3 appear to be swapped on your diagram if the batteries are to be in series. Please check in the manual BEFORE you make any changes based upon anybody's advice. \$\endgroup\$
    – mhaselup
    Commented Nov 14, 2020 at 4:36
  • 2
    \$\begingroup\$ 3&4 give 12v and 1&2 give 24v - you have done something wrong. Did you take a picture before you started? \$\endgroup\$
    – Solar Mike
    Commented Nov 14, 2020 at 5:16
  • \$\begingroup\$ It's not correct. But you need the UPS manual to find the correct arrangement; there is more than one possibility. \$\endgroup\$
    – user16324
    Commented Nov 14, 2020 at 13:39

1 Answer 1


Presumably you resolved this problem yourself, but I had trouble finding the answer elsewhere so here goes.

The SURTA2000XL has a 48v battery pack, so your diagram is correct except for battery 3 which has the + and - reversed.

If you plug a 24v battery pack into a SURTA2000XL and the UPS is live, it will attempt to charge them to 54v and cause smoke and possibly fire. From experience, this is not something you want to do =)


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