New version of Panasonic 18650 Battery has 2 bars – a narrow bar and a wide bar. But the old version only has one narrow bar on the PVC. If you see a Panasonic 18650 battery has dot matrix on its top, it must be very old and be manufactured before 2009.
No matter new or old version, the same date code rule is followed.
You saw the 4 numbers(sometimes numbers+letters) on the bottom of the battery? They indicate the battery manufacture datecode.
1. The first digit = year(0 = 2010, 1 = 2011, 2 = 2012, 3 = 2013, 4 = 2014, 5 = 2015, and so on).
2. The second digit = month(1 = Jan., 2 = Feb., 3 =Mar., 4 = Apr., 5 = May., 6 = Jun., 7 = Jul., 8 = Aug., 9 = Sept., 10 = X, 11 = Y, 12 = Z).
3. The third and the fourth together = day(01, 02, 03, 04….29, 30, 31).
According to the rules, the battery above is made on 2013-01-26.