It behaves the same way on internal battery, or connected to several different PCs and a powerbank (last one with 5V/2.4A output).
The other modem sees LTE network. On MIFI I get:
AT+COPS=?
+COPS: (1,"Vodafone CZ","Vodafone","23003",7),(1,"O2 - CZ","O2 - CZ","23002",7),(1,"T-Mobile CZ","TMO CZ","23001",2),(1,"Vodafone CZ","Vodafone","23003",0),(1,"O2 - CZ","O2 - CZ","23002",2),(1,"T-Mobile CZ","TMO CZ","23001",0),(1,"O2 - CZ","O2 - CZ","23002",0),(1,"T-Mobile CZ","TMO CZ","23001",7),,(0-4),(0-2)
OK
AT+CPIN?
+CME ERROR: SIM not inserted
(the SIM is actually inserted, but the modem does not recognize it)