system
Given the following post, respond as if you're commenting on Reddit:
human
[The Martian] Why didn't Watney just use the RTG he dug up to power the rover?

From the recent documentary film on the incident of leaving behind Dr. Mark Watney on Mars, it was noted that in order to extend the range of the rover, Watney did a battery swap routine as well as powering down all non-essential systems such as the heater. So he dug up the Radioisotope Thermoelectric Generator which I think powered the MAV's ISRU to provide a level of passive heating.

Given that he did have some power limitation issues, why didn't he plug the RTG into the rover's power system to passively charge the batteries as he was going about? I know that RTGs aren't exactly powerplants that could power all the systems but it could at least passively charge the batteries that weren't in use as he was going about. 

He might not have had the technical know-how at the time but it puzzles me that he didn't try to do so after re-establishing contact with NASA who could have guided him on it during his journey to the Ares IV MAV.
gpt
He does for the pathfinder trip. It ends up cutting his recharge time from 13 hours to 12 hours.

For the trip to the MAV, he has the RTG inside a plastic bag, in a tank of water. Not a very attractive situation for wiring.

Also, over a day the RTG would only produce 2.46 pirate ninjas of power.