Is my battery dying?

Hello!

I have a 2010 Prius IV and have a few things I want to attempt to take care of and avoid getting ripped off at the dealership. Also, the car has started not starting a few times during Covid lockdown. Would appreciate any help at all! I don't know anything about cars but I feel like I should be able to fix some of these things on my own.

1. Before March, I was driving my car every day with no issues. A few times recently after not driving it for a few days, the car won't start and all the warning lights turn on. Slowly the map turns on. After turning it off and attempting to start it again, after a few minutes it finally turns on, there are no warning lights and it drives fine. It did it again yesterday and today and this time I noticed that when I tried turning it on, the brake pedal went all the way down and it would not start. Then after waiting a few minutes when it did turn on, it seemed that the brake only went so far before feeling like there was something stopping it. Has anyone else had that happen? Does this mean my battery is about to die? I have 129,000 miles on my odometer. If my battery does need replacement, is this something I could do on my own?

2. My locking mechanisms stopped working a few years ago, the trunk still works but the other locks I have to lock/unlock manually. I got a quote for +/- $700 per lock (x4 doors). Is it possible to just replace the drivers door? I also lost one of the keys to unlock the door (I still have the plastic key holder, its just the metal key thing that pops out that I lost. How can I replace this?

3. I have a light out in one headlight, however the brights work just fine. The one headlight burns out and has been replaced several times. I have had a few people tell me that its an electrical thing.

4. The passenger seat belt is pulled all the way out and will not coil back up.

I appreciate anyone who is wiling to provide insight!

 

Thank you!