Batteries decay. They just do. A battery could be unused and essentially “brand new” in terms of use but have sat for so long it has decayed to the point of inefficiency. With batteries the more often you have to jump it back to life from zero the sooner the battery will go bad. You can really see this example with car batteries. Say someone has a starting issue and just decide to jump the battery when it dies. Well that battery will only be able to handle so many discharges/recharges before it just won’t hold a charge anymore.