Battery not holding charge while vehicle is off.

Hello, I just bought a used 2005 Prius. The car has 145,000 miles and I have a complete maintenance history, carfax, etc, and the battery was replaced by the previous owner last year with a GreenTec battery. I’ve noticed that while the car is off the battery will drain a bit, usually by only a couple bars but occasionally by a significant amount (only 3 bars left). It has no trouble recharging and will be mostly recharged in less than 5 miles, and will hold this charge fine while driving. I was wondering what the issue would be and how serious this issue is.

The remote is slightly damaged and taped together and I saw in another thread this could be triggering something when the remote presses itself, and therefore draining the battery, anything else I should look for? I was hoping I could rely on this car for at least 5 years or so since I’m a college student currently living paycheck to paycheck, so I’m really hoping it’s nothing major.