Why aren't my batteries discharging below 18%?

Undervalued

I use Lithium Polymer batteries, capable of providing high current, in a different field. For the best life I never discharge below 35%.

The optimum maximum discharge level will vary with different chemistries but unless you are absolutely sure I would err on the safe side.

Solarchaser

ispookie666 said:

How reliable is the SoC? Could it be the batteries are actually depleted ? 

Pylontech batteries are pretty reliable for reporting soc.
The uhome batteries are more questionable