Hi

I have 4 x 3.6kW Pylontechs coupled to an Axpert 5 mkii with 10 x 350W panels in two strings of 5 each. In every daily cycle I get a code 04 warning (battery low). I seldom get to the full charge at 53.2V. It ussually stops around 52V at the end of the day. As soon as PV charge stops I get code 04 at say around 49 - 51V battery power. It takes the whole night to get to say 48.5V when the PVs kick in again. Is this normal for Lithium Ferrous batteries. It seems that their band of operation is fairly narrow at 48V to 53.2V.

Regards

The Axpert inverter is known for not properly reading battery SOC, so it would be better to use a monitoring system like ICC, along with the Pylontech cable, to tell the Axpert what the actually volts are.

10 hours ago, Gellies said:

In every daily cycle I get a code 04 warning (battery low).

This is becoming a Frequently Asked Question.

Axperts aren't designed with LFP batteries in mind (despite what the marketing says). You have to set the battery cutoff voltage (usually setting 29) to a crazy low value like 44-46 V. The reason, in its lead-acid thinking, is that two whole volts above the cutoff voltage is where the battery is considered "low", and the low battery warning results. The warning won't come off until four whole volts above the cutoff voltage. As you've observed, an LFP battery is very flat in its voltage curve, ranging only 5.2 V from dead flat to end of charge.

The battery cutoff voltage also affects switching to and from mains and battery.

20 hours ago, SilverNodashi said:

The Axpert inverter is known for not properly reading battery SOC, so it would be better to use a monitoring system like ICC, along with the Pylontech cable, to tell the Axpert what the actually volts are.

Voltage is not a measure of power, so literally no inverter is going to be accurate with that input alone.  They can be "fine" tuned, but you need a shunt resistor and voltage over time to measure power consumption and thus effectively manage state of charge.