Yeah I just googled them and people seem to have figured it out but as you say they hide it on purpose. Some of them have stickers under the APC labels so you can peel them off as well.I got one of those UPS in front of me. Open it up to see what current the battery is. Genuine APC battery. Yet I can't find anywhere on the battery what it's current rating. Hidden on purpose so you buy genuine batteries likely.
The BX1500M is showing its needs a APCRBC124 not the RBC17 so its 2 batteries in a carrier. The only thing to confirm is you can get the batteries out of the carrier so you can re-use it. The batteries are nothing special though.
Yeah that would be my fear is that is going to be the new norm -- Sonic welding a carrier closed that cannot be opened without breaking it in order to make you buy OEM. Worst case you can buy ones in carriers from places like www.upsbatterycenter.ca (+Shipping or Amazon with the shipping built in) but it eats into the discount.The only time it gets wierd with the cartridges is sometimes how they 'bond' them together and at times fuse the batteries too. But if you're comfortable with disassembly and such, batteries are so easy and plentiful when you don't get them from the manufacturer.