receiver: use battery voltage in read_battery if available

lib/logitech_receiver/hidpp20.py

@@ -195,9 +195,9 @@ CHARGE_STATUS = _NamedInts(
 				error=0x07)
 
 CHARGE_LEVEL = _NamedInts(
-				average=0x00,
-				full=0x01,
-				critical=0x02)
+				average=50,
+				full=90,
+				critical=5)
 
 CHARGE_TYPE = _NamedInts(
 				standard=0x00,
@@ -513,10 +513,7 @@ def get_name(device):
 
 
 def get_battery(device):
-	"""Reads a device's battery level.
-
-	:raises FeatureNotSupported: if the device does not support this feature.
-	"""
+	"""Reads a device's battery level."""
 	battery = feature_request(device, FEATURE.BATTERY_STATUS)
 	if battery:
 		discharge, dischargeNext, status = _unpack('!BBB', battery[:3])

lib/logitech_receiver/status.py

@@ -229,6 +229,12 @@ class DeviceStatus(dict):
 				battery = _hidpp10.get_battery(d)
 			else:
 				battery = _hidpp20.get_battery(d)
+				if battery is None:
+					v = _hidpp20.get_voltage(d)
+					if v is not None:
+						_, charging, status, level, _ = v
+						status = _hidpp20.BATTERY_STATUS.recharging if status == _hidpp20.BATTERY_STATUS.recharging else _hidpp20.BATTERY_STATUS.discharging
+						battery = ( level, status, None )
 
 			# Really unnecessary, if the device has SOLAR_DASHBOARD it should be
 			# broadcasting it's battery status anyway, it will just take a little while.