Can't set proper battery alarms

[Srelliks]

Using INav 9 with Matek F450 and Radiomaster Tx15 with Lua display widget script installed. flying with a 8,000 mah 4s set up, I've put the battery in configuration as a 6,000 mah with alert at 20%, but fuel gauge display gets to alarm level after less than 800mah used (battery is good and voltage is still at 16v) and I get verbal alarms.

Is this a problem with the Lua script on the Tx15 or some other set up issue?

Any suggestions?