https://www.amazon.com/gp/aw/d/B0748D8KT6/

I’ve used this one. It’s a great “let sit” option and it was much smaller than I expected it to be. Used it over a half dozen times over a six month period without recharging it. Granted this was on a 4 cyl engine, but it still showed 80% charge at the end of 6 months so I imagine a larger engine would fare just as well. It did come with a cigarette lighter adapter, just not sure if you can leave it plugged in forever without damaging or degrading it.