Not tryin to be a naysayer, but
1. Aluminum is easily eaten away by battery acid.
2. Lawnmower charging systems are not designed for much of a heavy load. Putting big lights will drain the battery perhaps faster than the charging system can replenish. Put the battery on a float charger, after you are done using it hard, and it might not fry the charging system. Just my humble opinion, don't shoot the messenger.
3. That is some nice aluminum welding!