CyberPower UPSes with different VA but same battery pack?

[cptcrunch]

I'm trying to figure this out. I purchased an older CyberPower UPS, PR750LCDRTXL2U the other day. 750VA is a bit small, but in doing my research I see that the PR750LCDRTXL2U is the same chassis as the PR1500LCDRTXL2U, so I figured I could buy the 1500 batteries and install them into the 750 and have the bigger UPS at a cheaper purchase price (750s were cheaper than 1500s on eBay). Looking further, I see that the PR750, PR1000 and PR1500 all use the same battery pack. So I can't figure it out, if the 750, 1000, and 1500 all use the same battery pack, how/why are they rated for different VA/Wattage?

 

[mattventura]

Most likely, the battery isn't the wattage bottleneck for any of those three models. Instead, they're getting limited by the inverter or other hardware.