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Guide

Can my truck's alternator charge a camper's lithium battery?

Use a DC-DC charger per the maker's instructions. The 3 DC-DC chargers we list are rated at 40 A, 40 A and 50 A maker spec, so at most about 710 Wh per hour of driving at 14.2 V calculated. Data updated .

We don't cover charging through the trailer plug or a direct connection, and we don't size alternators, cables or fuses. Those depend on the vehicle and the wiring, which belong to the charger maker's manual and a qualified installer; see safety.

What the makers publish

ChargerOutputInput rangeEfficiencyWh per drive hour
REDARC BCDC1240D Dual Input 40A40 A9–32 VNot published by the maker568 Wh
Renogy 12V 40A DC-DC Battery Charger (RBC40D1U-G2)40 A9–16 V94%568 Wh
Victron Energy Orion XS 12/12-50A50 A9–17 V98.5%710 Wh

Smart alternators, in the makers' words

“Suitable for 12 or 24-volt vehicle systems, the unit will also work with either standard or variable/smart alternators.” (REDARC BCDC1240D Dual Input 40A)
“IGN signal wiring is required for smart alternators only.” (Renogy 12V 40A DC-DC Battery Charger (RBC40D1U-G2))
“An integrated mechanism detects whether the engine is running (engine shutdown detection), which only activates the charger when the alternator supplies power.” (Victron Energy Orion XS 12/12-50A)

The battery side

The charger's output must not exceed your bank's published max charge current. Each battery page checks every charger: see the DC-DC check, or put your rig and drive hours in the planner.

Sources