What happens if a 12 V DC, 7-ampere-hour battery is installed instead of a 12 V DC, 4-amp-hour battery in the Schneider APC PRO550?
The UPS will last longer before the battery runs out.
It might mis-report things like remaining time before the battery runs out or something, because it's expecting a battery of one capacity and you give it a higher capacity, but it will work just fine.