i am talking after experiencing my self in my santro,
in my car a/c delco of 90 AH was used & it last upto more than 6 years(car was on daily start running app. 100 km daily for 5 years)
there was not a problem single day of charging, always start on 1st attempt, even after 6 years, it was ok but car was sold( i told new owner gav him guarantee card & receipt that try ur luch=k,how many days it go more) so at least 6 years is enough to take out money from it