It was momentarily considered (further up the thread), however we opted for standard AA batteries as the primary power cell. Electronic design could easily be adapted to accommodate rechargeable AA batteries if the user wants a rechargeable option.
The energy capacity of AA batteries is also higher than typical lithium packs. A typical AA battery is 1.5v and 2800mAh (4.2W), while a typical lithium foil pack battery is 3.7v with an amp hour rating of anything between 180mAh and 500mAh. Typically we will need at least a stable 5v or greater voltage to operate certain components and the mechanics, so if we bank four AA batteries together in series we get 6v and 2800mAh, and with two lithium packs in series we get 7.4v and only 500mAh max (3.7W).
Ultimately, putting a lithium battery pack into the design means we would then have a specific custom sized battery into the design which needs replacing every few years, and sourcing this battery pack may become an issue in the future. To do right but our customers, we would need to then take it upon ourselves to source and manage the sale of battery packs for this lock well into the future - a burden neither party wants. Furthermore, the idea of either detaching the lock from the door to charge it over night, or bringing a USB cable to the door and let it hang there for a day… there just seems like a lot of down sides, and not any actual benefit over just using standard AA batteries that are easily replaced.
The only benefit I can imagine to adding a custom lithium foil power cell to the design is that it might possibly keep the back side of the lock casing just a few millimeters thinner… but in my view that’s not enough of a benefit to warrant this design choice. I’m up for discussing it though… I mean, am I missing a clear benefit to using a rechargeable lithium pack over user replaceable AA batteries?