How much is the projected cost of a replacement battery in the year 2018?

That's great that you love your car. If you figure normal inflation over the next six years a battery will cost anywhere from $55 to $265. This is the range from your cheap Walmart battery to the top of the line Optima gel battery.

I was talking about the main battery pack that when it first came out was $18,000 and now Nissan has it down to $9,000 for 2013.

Oh my bad, saw Nissan but not the LEAF part. Just an educated guess, but I would think they will go up in price as demand goes up. This is all hinged on the price of oil which is very unpredictable. ...................So that was not much help!!!!

Nissan has stated that their goal is to produce 2 times as many battery packs as vehicles to have a 2 to 1 ratio of batteries to cars by 2016. This is being done to lower the production and replacement costs of the battery packs. I am hoping for $4k to 5k range by 2018 to 2020.

They will for sure go down in price. I think that 4-5k will be the price point when it comes time to replace them. Just hope/pray that they go out under warranty so Nissan pays for the 2nd battery pack. Our Leaf is now 1 year old and the battery is getting better than worse so far!

Warranty covers battery under 60000 miles and five years, it's 4999 otherwise and less used.