Owntracks on Android (HTTP mode) battery level sent is Zero

Configuration
1

I put Hassio into Debug mode and found in the owntracks message the ‘batt’ attriute. I thought the the owntracks app does not send it at all. But why does it put zero ? The android’s ‘Battery optimization’ is disabled for the app on the phone. Should be ok. is it right? or the app send a value in MQTT mode only?

hassio’s log:

2019-09-25 13:29:16 DEBUG (MainThread) 
[homeassistant.components.owntracks.messages] 
Decrypted payload: 
{
"_type":"location",
"acc":16,
"alt":202,
"batt":0,
"inregions":["mol"],
"lat":99.9999555,
"lon":88.8888777,
"t":"u",
"tid":"u3",
"tst":1544444442,
"vac":0,
"vel":0
}