State of Charge (SOC) for Li-Ion vs LiFePo4

[kmxtornado]

I see that the state of charge chart for my 48v LiFePo4 shows 20% is 51.6v.
By contrast, a 48v Li-Ion battery at 20% is all the way down to 43.7v.

Why is that when both lithium chemistries start out at roughly 54.4v (at rest)?

The reason I ask is out of curiosity but in application, I'm wondering how far down I should be running my LiFePo4. The range is so tight. From full to 20% is only 3v. I'm sure there's a simple explanation. Can someone enlighten me?

 

[LewTwo]

LiFePO4 (aka LFP, Lithium iron phosphate) cells have a much flatter discharge curve than most other Lithium cell chemistries. You may also note that various manufacturers specify different Low Voltage parameters for LiFePO4. You really need a coulomb counter to determine an accurate State of Charge of a LFP battery.

Why is that when both lithium chemistries start out at roughly 54.4v (at rest)?

The batteries are designed for nominal 48 volts and at rest (fully charged) they will be slightly higher voltage.
The number of cells in series in the battery varies according to the chemistry.
For LFP (fully charged at rest): 16 cells x 3.25 volts per cell = approximately 52 volts.
(having said that I have LFP cells that measure between 3.35 and 3.50 volts when new)

Reference:
https://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery
https://batteryuniversity.com/article/bu-205-types-of-lithium-ion

This is a very long video about LFP cells, however there is a lot of good information in it.
Some of us (with thicker skulls) may need to watch it several times
https://youtu.be/QlDd3jkcxoQ