if your going to try and put lead acid batteries in that champion pallet pro pack you need to first see how the batteries are mounted. Some are mounted sideways (on their side) to save space. If this is the case you will not be able to use lead acid batteries.
secondly the charger may not be capable of charging lead acid batteries, you'll need to get the manual on that charger and see if it is, Some of those chargers can be dual mode and can be changed internally via a switch or jumper, some are not. The last pallet pro pack i dealt with did not have that capability.

From my experience dealing with these batteries they should meet the manufacturers specifications, using wally world marine batteries may allow you to get the battery pack back working but they are not classified as industrial standard and generally do not perform up to expectations over the long term. I would be hesitant putting those in there.

I know cost always plays a big part when dealing with batteries but in my experience trying to save a buck just doesn't pay off in these situations.