Caveat: I don't have any direct experience with this setup. But I think the smart setup might be to get a power bank that comes without batteries. Something like
this.
- Even if your batteries no longer hold a charge, the charger should still be good.
- As batteries get better, you can upgrade the charger.
- Similarly, if a better charger comes out, you can keep your existing batteries.
- If you need more capacity for a ride, bring extra batteries, not an extra power bank.
The one I linked to takes 4 × 18650 cells, but the same company makes 2 and 3 cell versions, and I can see other companies selling 6-cell models. So you should be able to calibrate it pretty closely to your baseline case.