I’ve been looking for the same to no avail. I’d buy one for my MacBook in an instant but the only things available in Germany are bulky hotspot devices with built-in batteries for 300-700€.
I'm almost sure this is the main reason for these dongles to not really have a market. A phone already provides the same functionality, the battery drain on a laptop would be pretty similar (since the modem on a phone is very well optimised) so extra power through a charger/external battery would be needed anyway if the main issue is draining the phone's battery, it'd just shift to draining the computer's battery.