Charging 12v battery with Bluetti power station

Running a 12v battery off a Bluetti is a bit of an odd one — you're essentially doing a DC-DC conversion with extra steps, and the efficiency losses can be significant depending on which output you're using.

If you're pulling from the Bluetti's 12v car socket, be aware most of these are limited to around 10A (120W max), which is fine for trickle charging but won't do much for anything above 100Ah in a reasonable timeframe. The DC output on newer Bluetti units like the AC200P is cleaner, but you're still burning efficiency going AC→battery→DC→battery.

Personally I'd question the whole topology here. What's the actual goal — keeping a leisure battery topped up in a static caravan or van? Because if so, a small dedicated solar charge controller feeding that 12v battery directly makes far more sense than routing through a power station.

That said, if the Bluetti is just acting as a temporary bridge — say you're waiting on a proper Victron MPPT to arrive — then connecting via the 12v output with an appropriate DC-DC charger like a Victron Orion-Tr in between would give you proper charge profiling rather than just shoving unregulated voltage at the battery.

What battery chemistry are you working with? AGM, LiFePO4? That changes the conversation considerably, especially around the charge voltages the Bluetti's 12v port will actually deliver.

Also worth checking: is the Bluetti's 12v output regulated or just a raw tap? Some units vary quite a bit under load.

What's your wider setup — anyone else here run this kind of config as anything more than a temporary bodge?

@PennineVanLifer done exactly this on the boat when I needed to top up a secondary bank without running the engine. The key thing nobody mentions is which output you use on the Bluetti matters enormously.

The 12v car socket output is typically regulated down from the internal battery voltage — more conversion stages, more losses. The AC inverter output going into a proper charger is counterintuitive but can actually be more efficient in practice, especially with something like a Victron Blue Smart doing the AC side.

Tested it myself with a clamp meter on both sides. AC route was losing roughly 15% end-to-end. The DC socket route was closer to 25-30% depending on load.

Not ideal either way, but if you're doing it, at least make the losses predictable with decent kit.

@FormerMariner36 snap — my boat setup has more "charging a battery to charge a battery to charge a battery" loops than a Rube Goldberg machine, but somehow it works when the engine's having a strop.

Done this on the narrowboat more times than I'd like to admit. The key thing nobody mentions is which output you use on the Bluetti matters enormously — the 12v car-style socket is often unregulated and horrible for lithium, whereas the AC output into a proper DC-DC charger (I run a Victron Orion-Tr Smart) actually gives you decent charge profiles and proper absorption stages.

Yes, it's AC → DC → AC → DC with efficiency hits at every stage, but when you're moored up and can't run the engine, sometimes "slightly inefficient" beats "flat battery." My Fogstar 12v bank doesn't seem to care, the BMS is happy, and the Victron handles the rest cleanly.

Horses for courses, really. If you're doing it regularly though, sort out proper solar instead.

@PeteJames yes, the output selection is everything. On my tiny house setup I made the mistake of using the AC output on a Bluetti into a mains charger — the conversion losses were genuinely painful once I actually measured it.

Switched to DC output direct into a Victron Orion-Tr and the difference was noticeable. Still not ideal but workable.

One thing worth flagging — check your Bluetti's DC output voltage range carefully. Some units wobble a bit under load and if your Orion or whatever DC-DC you're using has a tight input tolerance it can cause issues. Learnt that the hard way with a cheaper unit before I got the Victron sorted.

Basically treat the whole thing as a temporary bodge and size your losses accordingly rather than assuming nameplate efficiency figures.