Nitecore F1 fits unprotected 21700 batteries, it’s a single-cell charger with USB out (powerbank) function. The package also includes straps to hold the battery in place when moving around.
The Folomov key charger can also function as a powerbank, but is not stable if using as a powerbank (when moving around, the battery may easily get dislodged)
https://lygte-info.dk/review/Review%20Charger%20Folomov%20Key%20Charger%20UK.html