Yeah. Unfortunately even rechargeable pacemakers are extremely rare - almost all of them just expect that you'll have to replace the battery every several years (I think the average is 5?), which in the long run isn't terrible but still. Rechargeable batteries self-discharge far too much and as a result require quite frequent recharging so are far from ideal for implantation, although not having to undergo regular surgery to replace the battery is obviously a highly desirable outcome. The idea with internal power generation is to bridge the gap between the two and allow a person to go for far longer without the need for invasive surgery (there's a whole sidebar here about rechargeable battery chemistry not being ideal for implantation) but without the drawbacks inherent to rechargeable batteries.