@aismike I use my M7350 as a permanent hotspot for my car's high tech Infotainment dash module.. It is permanently pluged into the car's USB port for charging only. The data connection to the car is by WiFi.

The vehicle denergises the USB port when ignition is OFF, and as I seldom drive several hour journeys it never gets over charged.

It is a great MiFi, because it automatically switches ON when the car ignition is switched ON and a WiFi connection is established with the car completely automatically without having to phaff around like with my Huawei Mifi. It has worked like this for several years.

Replacement batteries are available on eBay, just search "ebay M7350 battery" . Simples !

I would add, if you are worried about over charging and overheating of battery, do not use a high grade USb3 cable as these will pass up to 2 Amp in quickcharge mode.!

Instead, use a cheap USB cable that will restrict the charging rate.

Most modern devices have self-charge-rate-regulation. So they throttle the amps according to state of charge and also time connected, Connected all day and they self throttle to trickle charging rate. I guess MiFi do not have this.