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
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)
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.
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.
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.