battery_features.py

In [112]: sql = "select timestamp, value from data where probe='edu.mit.media.funf.probe.builtin.BatteryProbe'"
In [113]: df = psql.frame_query(sql, con)
In [114]: df.index = pd.to_datetime(df.timestamp, unit='s')
In [115]: df = df.drop("timestamp", 1)
In [117]: ser = df.value.apply(json.loads)
In [120]: ser.values[0]
Out[120]: 
{u'health': 2,
 u'icon-small': 17303134,
 u'invalid_charger': 0,
 u'level': 23,
 u'plugged': 0,
 u'present': True,
 u'scale': 100,
 u'status': 3,
 u'technology': u'Li-ion',
 u'temperature': 346,
 u'timestamp': 1369294328.444,
 u'voltage': 3717}