Determining actual soc for lifepo4 power station?

[lostinabox]

More specifically, this is for the bluetti eb70. The battery display on this thing is very inaccurate. Enter my mini freezer which has a voltage readout.

When fully charged, the freezer will show the eb70 at 14.8v, same as when plugged into the wall. Fast forward, the battery display is reading as empty when it should stll be mostly charged. Right now, not running, the freezer is showing 13.4v. While running, the voltage will read between 12.6 and 12.8.

Can someone help me make sense of this?

 

[snoobler]

14.8V is an "absorption" voltage where the battery is held to ensure it's fully charged. If your mini freezer says 14.8V, I would question its accuracy as the EB70 should not be charged above 14.6V. Once the charge current is removed, the voltage can drop fast. 13.4V is a very reasonable number for this especially considering the EB70 uses some of its own power to run the inverter and other circuitry. Even a teeny load on a LFP cell can pull it down quickly to 13.4V-ish.

You're seeing a voltage drop because when a load is applied, battery voltage drops in accordance with V = I * R (I = current, R = resistance).

Assuming that once the load is removed, the voltage rises, I see nothing obviously wrong with your situation except for possibly an inaccurate voltmeter on your mini freezer.

 

[lostinabox]

I see. I plan to run some tests once it's charged.

 

[Techman Solar]

@snoobler I agree. Voltage fluctates when charging/under load. SOC based on voltage can be a guessing game. Portable power stations (solar generators) therefore can be fairly inacciurate in terms of battery capacity. A shunt is more accurate but I've found only the more expensive generators have one installed.

Quick question: Is the 12v DC output port not regulated?

 

[lostinabox]

The 12v is regulated, i tested it multiple times with a multimeter. When i originally posted my question i had run the fridge using the ac port. I've returned the power station since, and now I'm kicking myself as i didn't pay closer attention when i used the 12v port.