Why these trucks need the capacity

The 5.9L common rail uses a grid heater that draws heavily on a cold start, which is why these trucks left the factory with dual batteries. The factory alternator covers that and not much more. Add a plow, an inverter, auxiliary lighting or an audio system and you are asking for current the charging system does not have.

Mechman builds direct-fit high output alternators for the 5.9L from 240 amps up to 370 amps, in cast and billet with a range of anodized finishes.

5.9L vs 6.7L

The 5.9L common rail ran through 2009 alongside the 6.7L introduced in 2007, so both engines were available in overlapping years. Confirm which engine your truck has rather than going by model year alone.

Choosing a battery

These trucks run dual batteries. Replace both at once and match them, since a new battery paired with a tired one is dragged down to the weaker one's condition.

AGM handles diesel vibration and the deep cycling of auxiliary loads far better than a standard flooded starting battery.

Don't skip the wiring

Dual battery setups mean longer cable runs and more connections, each dropping voltage under load. See our Big 3 wiring upgrade guide and Big 3 kits.

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