yfin - highly recommend that you get your battery recharged now - don't leave it sitting there discharged for 5 weeks, or it will almost definitely need replacing when your dad gets back.

Most wet-cell lead acid batteries bounce back reasonably well if you recharge them immediately after they become discharged. Leave it too long and it will begin to sulfate, which will shorten the lifespan and capacity of the battery.

It might be worth investing in a battery tender if you've still got a few months before you get home. That will keep your battery topped up between starts.

Good luck!