I supposed it's possible, but the starter and electrical system would have to have been designed, manufactured, and installed for use of a 6 volt battery.
Drop it off at any auto parts store. If you want to get paid for it you can take it to a battery store.
the magneto
totally
12 volt
yes.
price
no
I'm assuming its a riding lawn mower of some type. Our own lawn mowers of this type have an alternator in them that keeps the battery charged
12Volts
Yes. Just make sure to use a battery of the same voltage.
Battery is either defective or the charging system is not working properly.
lawn mover