For me, it’s an electric toothbrush. It doesn’t matter if you go with Sonicare or Oral-B, once you start using an electric toothbrush, regular toothbrushes don’t ever feel like they clean your teeth properly. The smooth plaque-free top layer of your teeth that you can feel after using an electric toothbrush can’t be replicated with a regular toothbrush.
While I agree that vendor lock in sucks, getting a universal standard open source tool battery is not likely to happen. I decided to go with the Milwaukee M18. They have a huge variety of tools available, and they all use the same interchangeable battery. I have a drill, an impact driver, a circular saw, and hedge trimmers.