The RBC124 may contain the right batteries to repopulate a BR24BPG or at least reload the ones that came with your UPS however I don’t think it would work in its existing configuration without further investigation. It really depends on how the battery pack is wired and brief googling didn’t turn up much in the way of wiring diagrams. Be safe and be careful. If something bad happens, it could catastrophically go bad.

Good luck!

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Can I plug the RBC124 into the back of the Back-UPS Pro 1500G to get a little extra run time?

You are very welcome for the information! Honestly, I’m not sure what we did before the web aside from the usual “Well if it doesn’t come off, pry harder! If it broke, well it needed replacing anyways” approaches.

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Thank you for the clarification. I’m sure this will help a lot of people.

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What did we do before the web?

Thank you for your comments. I really appreciate the additional info and I’m sure that this will help others in the same situation. One of the reasons I even wrote this article was because of the limited information on the backup expansion pack. There was almost no documentation to start with and all I could find were sites that wanted to sell you a new battery pack at almost the same price as what I paid for the UPS/Battery Pack combo. When I went to the Batteries Plus store, the guy there was really helpful with identifying similar and compatible products and many people I know recommend them for all their specialty battery needs. I’ll keep that in mind about the online ordering however shipping could be a killer.

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RE getting off the front and back covers: I found it easiest to pry from the bottom (there’s a notch that I got a flat screwdriver into with a little forcing and then just pried outward on the cover). With the bottom end off, you can slide the cover up toward the top and, if you’re lucky, just unhook the teeth of the top tab–or pry a little bit while pushing up (so the teeth on the tab mostly disengage.

Before I put it back together, I sanded off the back of the teeth on the snap-together-tabs at the top and bottom of the front and back covers. The effect of that was to make the flat back of the teeth effectively shorter: the teeth angle toward the point on their backs now too (it’s not flat for the whole height of the teeth now). Which minor adjustment, I hope, will make it easier to pry off another time.

I also noted that there are molded-in screw holes in the inside case (at least on my model): top and bottom; front and back–if you measured carefully, you could drill holes in the outside front and back cover and use a narrow self-tapping screw to hold the front and back on–and just cut off the frustrating locking tabs–or really grind down the back of the teeth so they’d just hold it in place so it’s easier to get the screws in. It wouldn’t be quite as smooth on the outside, with the screws there, but it looks like a moderately straightforward option to improve access to the guts. If I were going to do that, I’d want to use some washers under the screw heads because the cover does not have a molded-in hole to accept the screw and the face of the cover isn’t very thick.

One item that may be of interest to others, when I went to Batteries Plus, the guy basically said, if the battery is the same physical size, it’s almost certainly the right one; they had them in stock. The replacement batteries are widely available on line also (a lot less if ordered although I did not calculate shipping). If you search for BX1500 replacements, you’ll find the right size (generally sold on-line in pairs–with the intention of reusing the harness that is holds the main unit’s batteries together). The same batteries apparently work in either the main unit or the external pack.

The Batteries Plus fellow also told me that a good, fully charged, battery will show a voltage of at least 10 volts (they had a tester that would check the capacity, but the ones I took in were so dead they didn’t even register). So, if you take a DC volt-meter and put the positive end into the middle prong on the big plug (whose guts are illustrated in the later pictures), you can put the negative side in the prong on the left (or right–at least one side works), and check either the battery pair in the main UPS or the 4 in the external pack–you should get a reading of somewhat more than 20 volts (my best ones–which are still some years old, mind you) show around 25 volts. (I’ve got 4 of these units with matching external packs.) The ones I’ll work on next show around 20 to 21 volts–probably at least one of the batteries in those packs is no good or perhaps, as in the one I operated on today, a pair is no good.

With some extension wires/test leads, a place like Batteries Plus would be able to test the capacity of the dual battery pair in the main unit or the external pack itself to give you even more info–without actually taking anything apart (other than pulling the battery pack from the main unit–a simple no-tools job). That would at least let know what kind of life the batteries have (if the straight voltage test isn’t a it’s-definitely-dead reading). Based on what I know from testing batteries of other technologies (such a ni-cd or li-ion), a battery can still show a reasonable voltage, but not hold much charge. However, if it doesn’t give you the voltage at all, you’ve got a dead one.

(Thanks again for the pictures and carefully created text! So far as I was able to find, this is a unique set of directions.)

I agree with your post, I believe that the resistor and yellow wire are used for current sensing either for charge control or for safe-shutdown detection when the batteries have been exhausted.

That’s odd, maybe it is pack-dependent. In my configuration, it’s wired up to the GND connection. Not sure what the electrical difference is between the two configurations. Check this image for the proper wiring for this battery pack.

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