Kai puts Elena in the coma in I'll Wed You in the Golden Summertime which takes place June 23, 2013. She does not wake up until just before May 2019, when Bonnie somehow finds a way of breaking the spell.
It denotes the charge storing capacity of the battery. 6Ah simply means that it can provide 6A current for 1hr or 1A current for 6hrs.
mAh is the battery capacity in layman's terms. Today's smartphones have the average battery capacity of 2800mAh. That means that a 6000mAh power bank should fully charge up your phone twice and a tablet 1.5 times.