M1 Charging problems and external antenna doesn't work

Hello,

I do have the well known problem that the battery is not loading because of overheating. The M1 is in a room of 18 degrees so it's not even close to summer. Sometimes the M1 is loading without overheating within 3 hours but most of the times it lasts 9 to 12 hours because of all the overheating security stops. I can't tell why there's sometimes no problem because I can't see any difference.

I've read that when overheating appears you have to look at how bad the signal is because a bad signal is causing more heat. By the way, I tried three antennas, one was the Netgear-MIMO antenna, all three antennas had a gain of 2,5 to 7 dB but there was no change in RSRP, RSRQ and SINR at all as if the antenna wasn't there... In some cases the signal was worse then without the external antenna...

The M1 sometimes goes through four LTE/4G frequncies B1 (2100MHz), B3 (1800MHz), B20 (700MHz) und B28 (800MHz) every frequncy for some seconds but always stays at B3 after that even if this is not the best and not the worst signal.

B3 (1800MHz):

RSRP -109 (2 of 5 bars – fair) (down- and upload is still fine for me)

RSRQ -9

SINR 11

I bought a 2nd M1 to compare, the 2nd one choose B20 and had a bettter signal.

B20 (700MHz):

RSRP -90 (4 of 5 bars – good)

RSRQ -8

SINR 21

After a autoupdate of the firmware of the 2nd M1 it did choose only the B3 as the first M1 does. So both M1 routers do now stay at B3 and do overhead.

Firmware before autoupdate: NTG9X50C_12.06.12.00

Firmware after autoupdate: NTG9X50C_12.06.39.00

Can I downgrade the firmware to 12.00?

I'm interested why the M1 shows mainly the B3 frequency? Is it showing the worst of all available frquencies? Is it showing the frequency it is mainly working on? Why isn't it using the best?

What I also found out was that when the batterie is charging the SINR goes down from 11 to 3, when I unplug the power supply the SINR goes up again...

Many thanks

Markus