As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
On take off EMERGENCY LIGHTS/CABIN circuit breaker popped and emergency lights came on. Returned to MSP and landed uneventfully. Reset circuit breaker. Emergency light system test gave FWD L BATT LOW message. Replaced battery pack at forward left power supply. Emergency light system test OK. Aircraft returned to service.