Is the most powerful battery in a toothbrush, the Lithium-ion?

When I order a new device, it comes with a rechargeable battery that's appropriate for that device. Everything is rechargeable. Americans make nothing, but in Asia people do.
You can't make them pick a battery once and for all.

Regardless of where they are placed, lithium-ion batteries have the highest energy density, as measured in watt-hours per unit of weight or volume.

However, some manufacturers might choose put 10X as many lower energy batteries in a device. You have to read the specs.