Controller displays F08 – Battery voltage low, start inhibited or slow cranking

Safety first: Disconnect charger AC supply before working on DC connections. Wear eye protection when working around batteries.

• Measure battery voltage: With a multimeter, check the DC voltage at the battery terminals. Compare to MTU specifications (typically around 24 VDC or 12 VDC depending on system).
• Inspect terminals: Clean any corrosion from battery posts and cable lugs using a battery brush and appropriate cleaner. Tighten all connections securely.
• Check battery charger: Verify that the MTU-supplied battery charger is powered and indicating normal operation. Measure its output voltage and current. Replace or repair the charger if it is not maintaining proper float voltage.
• Load test batteries: Use a battery load tester to evaluate battery capacity. Replace batteries that fail the test with units meeting MTU’s CCA and capacity requirements.
• Check for parasitic loads: With the generator off, measure DC current draw. Excessive standby current may indicate a fault in the control system or accessories that should be investigated.
• Clear alarm and test start: After correcting issues, clear the F08 alarm and perform a manual start to confirm strong cranking and stable voltage.