On the AAA battery there should be a sticker with a single letter and a single number.  The letter represents the month that the battery was manufactured and the number represents the year.  See below.
 
A=Jan
B=Feb
C=March
D=April
E=May
F=June
G=July
H=Aug
J=Sept
K=Oct
L=Nov
M=Dec
 
0=2010
1=2011
2=2012
3=2013
4=2014
5=2015
6=2016
7=2017
 
Please keep in mind that the AAA battery warranty is not transferrable so it would be void if it was installed in a vehicle that you purchased.