You can do it...I dropped 70lbs after a couple years ago. I definitely feel better.

As for a Lithium battery be very careful what you buy. Charging can be an issue, and running an alternator can be as well. All of them have a max voltage they can tolerate and need to take that into account with an alternator. We have had very good luck with Go Lithium batteries and alternators with regulators turned down to just under the for the battery