The three sources
You can refill the battery three ways: from the sun (solar), from the engine while driving (the alternator, through a DC-DC charger), and from the grid when you plug in (shore power). Each shines in different conditions, so most capable builds include at least two.
Treat charging as a team: solar for daily trickle, the alternator for driving days and bad weather, shore power as backup. A big battery with only one weak source stays empty.
Solar
Panels on the roof are the quiet, everyday charger. A few essentials:
- Use an MPPT controller, not the cheaper PWM type. MPPT harvests meaningfully more from the same panels, especially in cold or partial sun.
- Panel wiring. Wiring panels in series raises voltage and suits MPPT and long runs; parallel keeps things working better under partial shade. Many builds compromise with a mix.
- Roof space is the real limit. Fit as much as fits cleanly; you rarely regret more solar.
- Portable panels let you park in shade and put the panel in the sun, a useful supplement.
Size the array against your daily use with the method in battery & solar sizing and the calculator.
Alternator (DC-DC charging)
Your engine is a powerful generator. A DC-DC charger (also called a B2B) draws from the starter system while driving and charges the house battery at a safe, controlled rate with the correct profile.
- If you move every few days, this often out-charges solar, and it works at night and in rain.
- Do not wire the alternator straight to a lithium bank. A lithium battery can pull more current than the alternator can safely give, risking overheating. The DC-DC charger exists to limit and regulate that.
- Size the DC-DC charger to your alternator’s capacity (commonly 20–50A units).
Always charge a lithium house battery from the alternator through a DC-DC charger, never by a direct connection. Direct connection can overload the alternator and skips the protection lithium needs.
Shore power
When you can plug in, at a campground or a garage outlet, a shore charger (often built into an inverter/charger) tops the bank up fast and runs your AC loads without touching the battery. It is the ideal backup for long stationary stretches, cloudy weeks, or running an air conditioner. Many builds add a simple shore inlet even if they rarely use it, just for insurance.
Combining sources
These sources coexist happily: the solar controller, DC-DC charger, and shore charger can all feed the same bank, each doing its part. Prioritize by your travel style, mostly-parked builds lean on solar and shore; frequent movers lean on the alternator. A battery monitor ties it together by showing what is actually going in and out.
If you can only add one source beyond solar, make it a DC-DC charger. It quietly solves the winter-and-clouds problem that leaves solar-only builds short.
Lithium charge profiles
Every charger (solar, DC-DC, shore) should be set to a LiFePO4 profile with the right voltages, not a lead-acid default. And remember the cold rule from the batteries guide: do not charge lithium below freezing without a heating provision, whichever source is charging.
Common mistakes
- Solar-only in a climate or season that cannot support it.
- Wiring the alternator directly to lithium instead of through a DC-DC charger.
- A cheap PWM controller leaving solar harvest on the table.
- Wrong charge profile, using lead-acid settings on lithium.
- No shore inlet, so bad-weather stretches leave you stranded.
Quick checklist
- Fit as much solar as the roof cleanly allows, on an MPPT controller
- Add a DC-DC charger if you drive regularly
- Never connect the alternator directly to a lithium bank
- Add a shore inlet and charger for backup
- Set every charger to a correct LiFePO4 profile
- Respect the cold-charging rule on all sources