Battery system with selective thermal management

A battery system comprising:

• a first battery group, the first battery group having a first energy capacity and being adapted to operate at a first temperature of less than 0 degree C.;
• a second battery group electrically coupled to the first battery group in parallel, the second battery group having a second energy capacity and being adapted to operate at a second temperature, the second energy capacity being greater than the first energy capacity, the second temperature being higher than the first temperature, the second battery group having at least a first battery segment and a second battery segment;
• a first heating module electrically coupled to the first battery group;
• and
• a thermal path thermally coupled to the first group and including a first thermal segment and a second thermal segment, the first thermal segment being thermally coupled to the first battery segment, the second thermal segment being thermally coupled to the second battery segment;
• and
• a control module configured to cause the first battery group to power the first heating module to transfer heat to the first battery segment via the thermal path if the first battery segment is at a temperature below a predetermined threshold level.

A method for operating a battery system, the battery system having a first battery group and a second battery group, the second battery comprising a plurality of battery segments electrically coupled to one another in parallel, the method comprising:

• receiving a signal for starting the battery system;
• determining a first temperature of the second battery group;
• if the first temperature is below a predetermined threshold:
• using and partially discharging the first battery group;
• selecting a first battery segment from the plurality of battery segments;
• heating the first battery segment using energy from the first battery group;
• charging the first battery and heating a second battery segment by energy from the first battery segment once the first battery segment is at an operating temperature.