Running OH2 on Raspi 3
Just wanted to get Informed via Telegram whan my Batterylevel is low (in this case i use Homematic-Devices).
Group i created
Group:Switch:OR(ON,OFF) Batterie_HM "Batterie Homematic [%d]" <batterylevel> (Batterie_HM)
Items
Switch Heizung_WZ_LowBat "Wohnbereich Thermostat" <batterylevel> (Batterie_HM){channel="homematic:HM-TC-IT-WM-xxxxxxxxxx:2#LOWBAT"}
Switch Helena_Battery_Wand_Rep "Helena Thermosat" <batterylevel> (Batterie_HM) {channel="homematic:HM-TC-IT-WM-W-EU:xxxxxxxxxxxxxxxx#LOWBAT"}
I can see the Group as expected in my Sitemap
Group item=Batterie_HM
I created a rule to get an Message via Telegram when my Battery is low.
rule "Alarm Batterie Homematic"
when
Member of Batterie_HM received update
then
if(triggeringItem.state == ON)
{sendTelegram("BotExampelt", "Die Batterie von " + triggeringItem.label + " hat nur noch wenig Leistung.")}
end
I can see my Group in the Sitemap and it also shows me the LowBattery Switch is on (Helena_Battery_Wand_Rep).
Now my Problem:
I expected to get 1 Message via Telegram when the Swtich turns on, but instead Telegram is sending me every Minute a Message with the LowBatteryReport 
Also i can see maybe a Problem is detected in the log
2018-08-05 12:23:02.672 [WARN ] [pse.smarthome.core.items.GenericItem] - failed notifying listener 'Batterie_HM (Type=GroupItem, BaseType=SwitchItem, Members=0, State=ON, Label=Sensorbatterien, Category=batterylevel, Groups=[Batterie_HM])' about state update of item Batterie_HM: null
java.lang.NullPointerException: null
at org.eclipse.smarthome.core.items.GroupItem.stateUpdated(GroupItem.java:373) [101:org.eclipse.smarthome.core:0.10.0.oh230]
at org.eclipse.smarthome.core.items.GenericItem$1.run(GenericItem.java:250) [101:org.eclipse.smarthome.core:0.10.0.oh230]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:?]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:?]
at java.lang.Thread.run(Thread.java:748) [?:?]
Can someone pls help ?
