Battery Testing Standards for Heavy Vehicle Fleets

Load testing applies a heavy electrical load to simulate starting conditions, directly measuring the battery's ability to deliver current. Conductance testing uses electronic signals to measure internal resistance without discharging the battery. Load testing is more definitive but requires a charged battery, while conductance testing is faster and can test partially discharged batteries.

AGM batteries should be tested monthly with voltage checks and quarterly with conductance testing, similar to flooded batteries. However, AGM batteries cannot be tested with hydrometers and may show different voltage characteristics. They typically maintain voltage better until near end-of-life, making regular conductance testing crucial for early failure detection.

A resting voltage below 12.4V indicates a battery needs charging or has diminished capacity. During a load test, if voltage drops below 9.6V at 70°F when loaded at 50% CCA for 15 seconds, the battery should be replaced. Static voltage alone isn't definitive - always perform load or conductance testing for accurate assessment.

Regular testing creates trend data that can predict battery life. Conductance testing showing 80-85% capacity typically indicates 6-12 months remaining life. Tracking degradation rates helps predict replacement timing. Most heavy-duty batteries show accelerated decline below 80% capacity, making this a critical replacement threshold.

Always test batteries individually, even when connected in parallel. One weak battery can mask its condition when tested as a bank and will drain the good batteries. Disconnect interconnecting cables and test each battery separately. Replace all batteries in a bank if one fails - mismatched batteries accelerate failure of the entire bank.