FP Hotspot that works well as a car mifi

I forget, does any of these 2 work well as car wifi?
Franklin R850 (Certified Pre-Owned) Sprint LTE hotspot $19.99 (was $179.99 new) with free shipping
Netgear Mingle (Certified Pre-Owned) Sprint LTE hotspot $19.99 (was $149.99 new) with free shipping

Requirement:

  • Runs off USB adapter (turns on when car is on)
  • Runs without battery installed (turns off when car is off, also prevents overcharging and overheating in summer)

Ohhh found a reference on the 850.

So, that report says the R850 will run without the battery-- Chelle mentioned a while back that her R850 ran fine without the battery, but I don't know if she mentioned auto-power-up on power applied.

I've seen reports that the Netgear Zing 771S will run without the battery installed, too. I'd take this with a grain of salt, since it appears to be the CDMA version of the AT&T Unite 770S, and that one seems to be specific to the unit-- some will run without the battery, and some will not.

I don't know about the Mingle.

Chelle confirmed that AT&T 770S works well as a car mifi.

https://www.nthcircle.com/forum/freedompop/278-freedompop-lte-sim-with-netgear-mifi-aircard-770s-at-t-unite

Yes, Chelle had success with her AT&T Unite 770S running without a battery. Mine will start, but not complete boot, without the battery installed-- it shuts down, and attempts to start again in a loop. I'm pretty certain that Chelle later tested a 2nd 770S that also failed to boot without the battery.

I think we ruled out firmware as the deciding factor. I tried several USB power supplies rated at 2.4 amps. I suspect that something in the charging interface inside the unit limits current to an amount that is barely on the cusp of allowing no-battery startup. If it can get over the current hump needed to start, it will continue to run without the battery. (Without re-testing, I think mine will complete boot perhaps 1 out of 8 attempts, and ran for a few minutes before failing & entering the bootloop again.)

It kind of matches up with mentions I've seen about the 770S and 771S-- some say with confidence that one will run without a battery. Others say with confidence that one will not. I've never had a 771S (Zing) to test.

If intermittent, then it could be insufficient voltage or amperage... I have some car adapters that will run the MiFi 500 and some that will not.

Insufficient current (amperage) is my expectation. But, since I'm testing with 2.4A power supplies (including a 16000mah power brick), and 2.4A is the max rating for USB power, there doesn't seem to be an easy way to increase the current I'm providing.
I suspect the problem might lie with current limiting inside the hotspot itself, possibly to prevent overcharging, and that the full current I'm providing never reaches the hotspot.

R850: The hotspot has LTE bands 2/4/5/12/26/41, but no 3G.