As far as I can tell the CyberPower batteries HR1234w and bp8-12 are the exact same size batteries, and both have F2 terminals. So I’m not sure why you would need to buy more than one type of battery. Next time I will try buying the biggest AH rated 12 volt battery that is the same size. The size of the batteries was (by my micrometer, and body only no terminals): 3.68 inches high, 2.54 inches deep, and 5.94 inches wide.
When I purchased the CyberPower replacement battery for the 850AVR (with lcd) it was stated to be a 12v 9ah battery, and the CyberPower replacement for the 1350AVR (with lcd) was a pair of 12v 8ah. There is definitely no need to do anything more than buy a pair of the 12v 8ah batteries off Amazon for $30 instead of paying $76 for CyberPower’s new assembly. Just make sure you plug the cable in correctly on the new set or you may have a very unfortunate incident. Next time I plan to just use some packing tape to put the new batteries together. The CyberPower part number for the 1350 was RB1280X2A. The CyberPower part number for the 850 was RB1280A. Based on the part numbers it is easy to believe they they are both 12v 8Ah batteries.
In case you didn’t know lead-acid batteries should not be put in the garbage. Lowes and Home Depot accept non-automotive sealed led-acid batteries for free. So, just drop them off there.