You need to tick the “Processed fit file messages” box and use a script:
{
let level
for (let di of icu.fit.device_info) {
if (di.manufacturer?.value !== 23 /* Suunto*/) continue
console.log("di " + di)
let v = di.battery_level?.value
if (typeof v === 'number' && (!level || v < level)) level = v
}
level
}
In this case I have chosen the lowest value. The console log looks like this:
di timestamp(s)=1075909291,battery_voltage(V)=4.05078125,battery_level(%)=70,manufacturer=23,product=59,product_name=Suunto Vertical
di timestamp(s)=1075909479,battery_voltage(V)=4.05078125,battery_level(%)=69,manufacturer=23,product=59,product_name=Suunto Vertical
di timestamp(s)=1075912229,battery_voltage(V)=4.03125,battery_level(%)=68,manufacturer=23,product=59,product_name=Suunto Vertical