Repairs Cub Cadet LT 1045 with replacement Briggs IC twin turbo 18.5 HP

I just bought a Cub LT 1045. The person I bought it from replaced the Courage engine with a Briggs IC 18.5 HP. I try to start this mower and it gets 2/3rds of a crank and acts like my battery is dead. This battery had just been fully charged prior to start up. The battery I used came out of a my old but working Craftsman mower. At the the first attempt to start up the battery caps spit water/ acid out of the caps. Do I have a dead short creating this and if so where do I start to track down my issue? Just an FYI if i jump it it will run fine until I shut it off. If I don't try jumping it on the restart it wont crank over and I am back to my initial issue.

Have you resolved battery issue? Try this first, tilt hood & with both hands on top of engine screen rotate engine clockwise just past hard spot & try cranking with key, if it starts you need to adjust valves with engine cold. If not, remove battery & take to auto parts store & have them load test battery, this will let you know if battery is good or not good. If you have to purchase a new battery make sure it is fully charged and at least 230 cca's. Next check by hand all wiring & connections for corrosion, being tight & secure, also ground cables & straps. Post numbers from B&S engine, model xxxxxx, type xxxx, trim xx. You need to check & adjust valves on B&S engine.