Battery Problems?

I just bought a used 2013 Prius C yesterday at 129k miles and drove it 300+ miles yesterday because I got lost on the way home. For the first 150 or so miles on the highway I got 55 mpg, and then when I stopped the car to get gas I was only getting around 46-49 mpg for the rest of the trip. I'd assume that during this time, the battery got fully charged and was good to go (I wasn't paying significant attention to it but I know that throughout most of the trip it was fully charged). The lower mpg was on the final stretch between Chicago and Champaign Illinois which is known for being extremely flat.

After I got home last night, I took my car about a mile away to a vet for my sick Great Dane mix puppy to get checked out (who absolutely loves the back seat of the C and fits comfortably). I don't remember looking at all at the battery since this was around midnight, but when I moved my car from the front of the house into the garage this morning to detail it, the battery was at 2 bars out of 6. I'm really new to this car so I don't know if that's unusual or if my car is having battery failure? The lower mpg of the car was also driving at night, but I don't really know how the headlights operate either... I know the side goes from 0 - ? - buttons - brights, but if I accidentally left the headlights on the second (between no lights and buttons lit up) setting for an hour while at the vet, would that drain the battery? I know the car beeped at me for trying to leave with the buttons on, but it didn't beep at me with it on the second setting. I know that the headlights were also very dim at night and difficult to see with so much that the brights were about the level of the headlights of most other cars on the highway it felt like. I'm an electrical engineer so I feel like I should have a better idea of what's happening, but I'm completely new to the hybrid scene and have no clue what to expect. I know the previous owner hasn't driven the car much at all (<10k miles) since the pandemic because they are still work-at-home and bought a newer more expensive car. All the work has been done at the dealership and the battery has always tested fine and the mpg doesn't feel unexpected either. I'd categorize the acceleration as being slow, but definitely not slower than any other Prius I've handled (again, I've really only driven around a couple of them mostly with friends who have prii or on test drives and not any beyond 2010).

I'm buying an adapter to use the Dr. Prius app to check the resistances and voltages on the battery, but is it worth investing in something like a Prolong battery reconditioner? I travel solo a lot with my dog for my skydiving career and a lot of extreme sports/trail marathoning and I really don't want to come back after a few days to a dead Prius...

Update: I just figured out the headlights situation oops, it would make sense why I thought the "brights" looked like normal headlights... Not sure if daytime running lights would stay on after turning off ignition/leaving the car but that would certainly explain the battery if they did...