Disclosed herein are battery systems for electric vehicles. An electric vehicle may include a first battery. The first battery may be configured to power various low voltage systems. For example, the first battery may provide the power to start the vehicle. The vehicle may include a second battery. The second battery may be configured to power one or more electric motors for propelling the vehicle. The first battery may include a housing. The housing may include a battery monitoring system. The battery monitoring system may include a PCB that is secured to at least one bus bar. The bus bar may include an integrated shunt. The shunt may be coupled to circuitry on the PCB that is configured to monitor current.