From embeddedTS Manuals

The TS-8820 provides 2MB of battery backed static RAM. The RAM is accessed through a 4KB memory window. After programming the SRAM page register, 16 bit reads or writes can be performed to any part of the page.

This can be accessed through ts8820ctl:

echo "test" | ts8820ctl -W 5
ts8820ctl -R 5
Note: The SRAM is not populated by default. See U16 to verify the presence on your board. If you require battery backed SRAM please contact us.