Starting issues and power saver mode

So, last week I went to start my 2013 ford fusion and the dash lit up but when I pushed the button, it just clicked and I got a run power active warning. My buddy jacked it up, tapped the starter with a hammer and it started but I had an engine light on. I ran for a bit at highway speeds, took it home, turned it off and let it sit for a bit. I restarted it no problem and the engine light was off. A couple days later, same problem with it not starting, did the same thing all over again. Only thing different I noticed was that before it started again, the nav screen showed it was in battery power saver mode. Once it reset, car started no problem. Booked it into the shop, they ran all the tests but because there was no engine light now, nothing showed. So they just replaced the starter.

This morning, I get into the car and before I press anything, the nav screen shows the battery saver mode. I wait for it to load fully and it starts. My question could this possibly a battery issue? My buddy tried jumping the battery the first time it wouldn't start and that didn't make a difference but hes not positive if his cables are working. My real fear is that its the alternator and I worry about spending more money on things that dont need to be replaced. They didn't even mention it at the shop but it was a super busy day so I didn't even get a chance to talk to the mechanic

Anyone deal with this before?