Charging a power station from the car: 12V socket vs alternator charger

For most trips the car's 12V socket is enough only if your station is small or you're driving for hours. It puts in about 100W, which tops up phones-and-lights stations nicely but takes around 12 hours of driving to refill a 1kWh unit. If you drive most days and run a 12V fridge off the station, an alternator charger is the one that keeps up. EcoFlow's does up to 800W and Bluetti's up to 560W, which turns a few hours on the highway into a near full battery.

The specs below come from the makers' Australian pages and manuals. The charging times in our worked examples are our sums, with a 15% charging loss that's our assumption, not a measured figure.

Why the 12V socket is slow

A car's accessory socket is a fused circuit built for phone chargers and fridges, not for refilling a kilowatt-hour battery. Bluetti puts a 12V vehicle socket at around 100W and a 24V truck socket at about 200W. Elsewhere on its Australian site it says 80 to 90W at 12V, so treat 100W as the best case.

The station limits it too. EcoFlow's manual rates the EcoFlow DELTA 3 Plus car input at 12V and 8A, which is 96W. Anker lets the Anker SOLIX C1000 take up to 10A below 32V on its XT-60 input, so about 120W at 12V if the socket can supply it. Both come with a car charging cable, so this costs nothing extra.

EcoFlow's manual also says to plug the cable in after the engine's started, so a weak starter battery isn't asked to do two jobs at once. We'd go further and only charge from the socket while you're driving. Running the engine at a campsite to charge a station is slow, noisy and burns fuel for very little energy.

What three hours of driving gets you

Here's the sum for the socket. A DELTA 3 Plus drawing 12V at 8A takes 96W. Allow 15% lost to heat while charging and about 82W reaches the battery. Three hours of driving is 82 x 3 = about 245Wh.

A full refill of its 1,024Wh battery is 1,024 / 82 = about 12.5 hours. On a weekend trip that's the difference between topping up and starting each night half full.

Now the same drive with an alternator charger. At the Bluetti Charger 1's 560W, less 15%, that's 476W into the battery, so three hours would be 1,428Wh. In practice the station fills well before that. Bluetti says the Charger 1 fills a 1kWh station in about 2.5 hours. With the EcoFlow 800W Alternator Charger, 800 x 0.85 = 680W, so a DELTA 3 Plus would take 1,024 / 680 = about 1.5 hours. EcoFlow's own figure is 1.3 hours, which assumes less loss than we do and a vehicle that can supply the full 800W.

What an alternator charger is

An alternator charger is a DC-DC charger built for power stations. It's wired to the starter battery with heavy cable, takes the vehicle's 12V or 24V and steps it up to the higher voltage a station's input wants. EcoFlow's unit takes 11 to 31V in at up to 76A and puts out 40 to 60V. Its FAQ gives the input as 11 to 35V, so check the manual for your version. Bluetti's Charger 1 draws up to 50A from a 12V system (25A on 24V) and outputs 15 to 56V, which you set in its app.

They connect differently. EcoFlow's plugs into the extra battery port (XT150) on DELTA models and mainly suits EcoFlow stations, with an XT60 output cable sold for other brands. Bluetti's feeds the station's solar input through MC4 plugs, and Bluetti says it works with its own stations and most other brands. The Charger 1's default output is 27V, so you'll need to raise it in the app to get anywhere near the full 560W, as long as your station's solar input can take that voltage and power. The Bluetti Elite 100 V2 is listed at up to 1,000W of solar input, so it can.

Both chargers only use what the alternator has spare. EcoFlow says the charging power depends on the alternator's surplus and may fluctuate, and that alternator capacity varies by vehicle, so check yours can supply the draw. Pulling 70A at 12V is a lot to ask of a small hatchback's alternator that's also running headlights and the air con. Both list undervoltage protection so they stop before flattening the starter battery.

Getting one fitted

These run off the vehicle's 12V system, not the 230V mains, so it's an auto electrician's job rather than a house electrician's. EcoFlow says the install isn't complicated but recommends a professional workshop, and that cables should be kept clear of hot, sharp and rubbing spots and fastened so they can't work loose. Bluetti says most people can fit the Charger 1 themselves with the supplied cable. The current involved is high (EcoFlow fits a 125A fuse), so if you're unsure about fusing, cable runs or mounting, have an auto electrician do it. If your 4WD already has a dual-battery system, tell them, since the new charger has to share the same alternator.

Heat and the car

The Queensland Fire Department says to keep lithium batteries away from direct sunlight and heat, and not to charge or use one that's hot or showing damage. A closed car in summer is the opposite of that. EcoFlow gives the DELTA 3 Plus a charging range of 0 to 45°C, and a car parked at the beach goes past that quickly. Keep the station out of direct sun, with air around it, strapped down so it can't slide, and take it out when you park. If it's hot to touch, stop charging and let it cool.

On a trip, the socket is a useful backup to solar rather than a replacement. Our caravan and camper sizing guide works out what you need to put back each day, and solar panel pairing basics covers the other half of the recharge plan. To check how long your own fridge and lights will last between drives, use the runtime calculator.

Where to buy in Australia

Buying from the brand's Australian store means 230V AU outlets, the local warranty and local support. Prices move around a lot, so check on the day.

• EcoFlow 800W Alternator ChargerEcoFlow AustraliaSee it at EcoFlow Australia
• Bluetti Charger 1 (560W)Bluetti AustraliaSee it at Bluetti Australia