The Pocket Modem is draining faster than it is charging. What to do?

Question

Iron

Good afternoon to the collective mind.
Not so long ago I got hold of a pocket modem MegafonMR100-3 (aka Huawei E5372). Absolutely happy with everything, knocked out an unlimited tariff for 1000 rubles / month, but that's not the point.
This week I began to use it actively and by the evening of the second day I noticed an extremely unpleasant nuance - even when connected to an external battery (5 V, 2.1 A) or to a laptop (Macbook Air mid 2013), it discharges faster (sic!) than it charges. At the same time, I tried to minimize the load (connect only one device via wifi) - nothing. Anyway, the discharge process is faster than the charging process. I tried to leave him a "buffer zone" in the form of 15 minutes of charging in the off state. As a result, he worked 20-24 minutes and died again.
Battery characteristics:
HB5F2H 3.7V 1780 mAh (6.6Wh)
Maximum voltage: 4.2 V
If you start charging it from the moment you turn it on, it lasts about 7-8 hours, but something tells me that such a "stream" use of the battery will not lead to anything good. I would welcome any thoughts on the topic. Thank you.

Answer 1

The charging cable also matters ... Try changing the cable to a more serious (thick?)

Answer 2

If the battery is discharged during charging, it means that charging does not take out the battery + modem. Try changing it to a more powerful, at worst battery.

Answer 3

bought a new one enough for a day, no longer happy, worse than a smartphone!

Answer 4

1) Turn off Wi-Fi and use the Internet by wire.
You can distribute it to a mobile / tablet from a laptop, preferably via Bluetooth - it is less gluttonous.
2) If there is no LTE (4G) coverage - turn it off, leave only one range by turning off auto-selection.
3) Use an antenna if the router is always in the same place.
4) Buy a spare battery