This page contains affiliate links: if you buy through them, we may earn a commission at no extra cost to you. How we choose.
Rig Amps may be paid through affiliate links to Renogy, EcoFlow and BLUETTI. As of November 7, 2026, no affiliate program has accepted the site yet, and Battle Born links (which sell the Victron chargers below) never carry a commission. Affiliate disclosure.
Driving is the most reliable charging you have in winter: the alternator works in the rain and at night. A DC-DC charger (also called battery-to-battery or B2B) sits between the starter battery side and the house battery and controls how much current flows and at what voltage.
What it does
- Isolates the batteries: the house battery cannot drain the starter battery.
- Charges with the right profile, lithium or lead-acid, whatever the alternator voltage.
- Limits the current to its published current, which protects the alternator and the wiring sized for it.
How much it puts back
Wh per hour of driving ≈ charger amps x 12 V
A 30 A charger gives about 360 Wh per hour of driving, a 50 A one about 600 Wh [calc]. With the 1,440 Wh worst-case fridge day, that is 4 hours or 2.4 hours of driving [calc]. With EcoFlow's 165 Wh fridge day, under half an hour at 30 A [calc]. Your power budget tells you which case you are in: power budget.
Chargers in our check
| Charger | Published spec | Charges | Price |
|---|---|---|---|
| Battle Born Victron Orion-Tr Smart 12/12-18A isolated | 18 A, 220 W | house battery | $143.65 |
| Renogy DCC30S 30A DC-DC with MPPT | 30 A | lithium / lead-acid house battery | $186.99 |
| Renogy 40A DC-DC with MPPT | 40 A, 616 W | house battery | $205.99 |
| BLUETTI Charger 1 (560W alternator charger) | 560 W | BLUETTI power stations | $219 |
| Battle Born Victron Orion-Tr Smart 12/12-30A isolated | 30 A, 360 W | house battery | $219.30 |
| EcoFlow 800W Alternator Charger | 800 W | EcoFlow power stations | $269 |
| Renogy DCC50S 50A DC-DC with MPPT | 50 A | house battery | $307.99 |
| Battle Born Victron Orion XS 12/12-50A | 50 A, 700 W | house battery | $328.10 |
How we compare: criteria, sources and dates
Specs as published (amps in the product or option name, or watts on the page). Victron chargers are sold here by Battle Born. Prices read November 7, 2026.
MPPT solar controllers
If the DC-DC charger has no solar input, the roof needs its own MPPT controller. Size it on the 12 V solar limit the page publishes, not only on the amps:
| Controller | Charge current | Max solar at 12 V (published) | Price |
|---|---|---|---|
| Renogy Rover Li 20A MPPT | 20 A | not published on the page | $87.99 |
| BougeRV Sunflow 30A MPPT | 30 A | 450 W | $109.99 |
| BougeRV Sunflow 40A MPPT | 40 A | 600 W | $139.99 |
| Renogy Rover Li 30A MPPT | 30 A | not published on the page | $149.99 |
| BougeRV Sunflow 60A MPPT | 60 A | 900 W | $169.99 |
| Renogy Rover Li 40A MPPT | 40 A | 520 W | $205.99 |
| Renogy Rover 60A MPPT | 60 A | 800 W | $399.99 |
How we compare: criteria, sources and dates
The roof tool picks the cheapest controller whose published limit covers your array, and the battery comparison lists the house batteries.
Installation. A DC-DC charger connects to the vehicle's starter circuit and carries high current over the length of the van: cable size, fuses at both ends and the vehicle's alternator limits all matter. Have it installed by a qualified installer, follow the charger and vehicle manuals and, for RVs, NFPA 1192.
Frequently asked questions
Do I need a DC to DC charger for a lithium battery?
In most modern vans, yes. The alternator's voltage is set for the starter battery, and on vehicles with a so-called smart alternator it varies with the engine's needs. A DC-DC charger takes what the alternator gives and charges the house battery with its own profile, including LiFePO4.
What size DC to DC charger do I need?
Amps x about 12 V gives the charging power: 30 A is about 360 W, 50 A about 600 W [calc]. One hour of driving at 30 A puts back about 360 Wh. Larger chargers draw more from the alternator and need heavier cables; the vehicle and charger manuals set the limits.
DC-DC charger or alternator charger for a power station?
A DC-DC charger charges a fixed house battery. EcoFlow's 800W Alternator Charger and BLUETTI's Charger 1 (560W) are made to charge those brands' power stations from the alternator.
Can a DC-DC charger also take solar?
Some can. Renogy's DCC30S and DCC50S have an MPPT solar input; the 50A model lists "Max. Solar Input Power | 660W @ 50A".