5v battery to a device with a 7.4v output? : r/batteries
A 7.4V output from a battery indicates that it''s just two 3.7V lithium-ion cells in series. A cell is considered empty at 3.0V and full at 4.2V. This gives the two cells in series a voltage range of 6.0V up to 8.4V. So you can supply the heated gloves anywhere in that voltage range and it should be happy.