You don't even need to go that far with the on-board hardware. Just track battery exchange history with charging pattern data, and identify offenders.

Bad actors can spoof the battery charge reader, but it's much harder to spoof the juice out of the charger.

Battery tracking leads to ads. Ads lead to the dark patterns of the force.

I uh, don't see the point?

You have the charging electronics which will tell you very quickly when a battery is dead, and you know which subscriber gave you the faulty battery. Sure faulty batteries can happen naturally (and accidentally), two faulty batteries though should be statistically enough to trigger an investigation from the company.

I think the idea is that the battery reports voltage like a mostly charged normal battery for just long enough for you to leave the scene with a good battery.

Ideally this would be coupled with lax device receipt keeping so while the company could tell that one of these thousand customers that used the kiosk that day returned the faulty battery it'd be hard to pinpoint a specific wrong doer.

That said, it feels like the margins on this would be low enough to make it not worth the effort.

You could take a legitimate battery and swap good cells for cheaper or old cells. The actual cells usually don't have any smarts to them and would still show as having a full charge but the range would be limited. It could take at least one depletion cycle for the processor inside to realize the cells are of poor health and may just look normal to untrained eyes. Proper security would include soldering batteries in, welding the plastic seams shut, or adding tamper indicators in the battery like a switch on the lid. The system could just refuse to charge any tampered batteries or the attendant could refuse to swap any batteries that have obvious damage.

A lot of battery controllers are intentionally designed to make the batteries unusable if the cells are removed for even a moment. Sometimes the controller uses a volatile ROM that wipes itself when it loses voltage, other times there's software actively looking for it and stopping the controller from working when detected. It's very consumer unfriendly in general for batteries that the consumer supposedly owns, but for batteries that are more loaned property like this it's a reasonable anti-tamper system.