The i-Sense battery should be replaced every 2 to 3 years.
What type of battery is used in an i-Sense?
There are 4 batteries in an i-Sense that look like standard AA cells, but they are NOT.
Do not put standard AA cells in your i-Sense. The batteries for the i-Sense cannot be bought at
your local store. Here are the specifications:
2000mAh to 3000mAh
One location that has these batteries is www.batterystore.com. There are others.
How do I replace my i-Sense batteries?
Find the battery cover on the bottom of the i-Sense unit
Loosen two Phillips-head screws and remove the battery cover to access the battery holder
Carefully disconnect the battery plug and pull the battery holder straight out
Remove and recycle the old batteries
Install fresh batteries making certain that the battery polarity is correct