Well, thats easy to calculate but depends on your personal usage.my September one is dated 07-2017.my yesterday received one is 05-2017...............
Shit! so the point of change would be 07/08-2017, is my guess.
Curious how many bowls you can do on a charge.
For example I can do about 6 large bowls per charge. 6 / 5 (20%) = 1,2 so I could have just one more bowl. Nice to have but not nessessary.