istick 30w replacement – ideas please?

I have an eleaf istick 30, and use it with a Nautilus mini, MTL. The istick is not holding a charge, and I need to replace it after a couple of years of heavy use.

I'm sure there's better products out on the market now – but I'm not up on them.

Suggestions for a simple (no external batteries, i just like to charge and that's it….no fussing) replacement?