MTD no start

Sold my Powr kraft but now the guy who bought it to mow has an issue, he can't start the tractor. It has an older battery, which might be the culprit, or my diagnosis is that the charging system is dead. (Headlights are dim, are hooked straight to stator) Has a briggs and stratton 18 hp opposed twin. Think this is the issue?

Still cranks, but really slowly.

Only one way to find out, put on a new battery and see...! lights will always be low at low speed.