I don't have an Ecoflow, but I have a small Allpowers PowerStation and a larger VTOMan 1500X Power Station. With those units - and I think most Power Stations (including at least some of the EcoFlows), the 12V DC output is very limited - typically 10A - and may not provide enough current for your needs?
Neither of my Power Stations would power my DC Air Pump to pump up my Kayak or SUP as the pump draw 11A.
Very frustrating have to say as for example the VTOMan as a 1500W continuous output
Inverter, so when that is running, it is happy to send over 100A (12V equivalent) from the
Battery to the
inverter but can't deliver more that 10A @12V to a socket. If I want portable power for the pump, I have to plug a
battery charger into the VTOMan and then connect the output of that charger to the Pump. Converting DC to AC and back to DC again. Wasteful.
I think there are a couple of issues with this "Direct to
Battery" solution that makes it NOT a solution.
The first is as described above - the internal DC-DC converters within the power stations are rated too small to be very flexible in their output. You might find you need to have the power station connect via its
inverter to the EHU input to provide enough power?
The other is more fundamental - the 12V DC outputs on a Power Station are regulated. They output a certain voltage suitable for driving 12V devices and not suitable for
battery charging.
My AllPowers outputs 13.10V. That is actually a bit too high and I think it would likely drop significantly when a load is applied.
My VTOMan (a better quality unit than the AllPowers) outputs 12.3V.
The way DC current/charge flows is from a higher potential to a lower potential - so if you were to connect a Power Station DC output with say a 12.3V potential (such as my VTOMan) to a fitted Leisure
Battery, you would only get power drawn from the Power Station if the Leisure
Battery was below 12.3V. If that Leisure
Battery was a Lithium one, the only time you would get a voltage that low on it was if it was close to fully discharged. Your next problem is that Lithium Leisure
Battery if below 12.3V will try to take so much power from the Power Station it would exceed the DC Socket Rating and you would end up with a blown
fuse very quickly - and if that blown
fuse was inside the Power Station ... now you're buggered! If the Lithium Leisure
Battery is so dead you need to use the Power Station, you will need a way to disconnect the Lithium
Battery (maybe a switch. maybe a BMS setting via Bluetooth?)
Overall a major faff and not a simple "connect it to the
battery" solution. IF it was a 12V
Battery in a box then yes, that was doable, but these all-in-one Power Stations have their own built-in limits and problems.