I use an electric toothbrush. Actually two, one for the main brush, one for the fine brush. They are battery powered, using AA batteries. That's preferable to the kind that has a built-in battery, because when the built-in fails, all you can do is throw the entire thing away.
The steel core that engages the brush, can get rusty. I think it's nickel-plated, but still it rusts. So once per year, I take off the brush heads, give the shafts a good scrape, and then coat the shafts with Vaseline. This preserves them against rust for another year.