I was hoping there would be a 100% sure way that a 13-15 batteries would fit but few of the responses have mentioned there could be some problems getting it to work on a 11 leaf.
I don't want to spend $3k on a used battery only to find out it's not working. Then I would have to spend another $3k to get 11-12 battery pack. That means I would end up spending $6k for two used batteries where I could just by a brand new battery pack. Sometimes being frugal costs more in the long run
I'm ok if the new battery degrades in the future, hopefully I'm planning on buying a Tesla which has a BTM. Even the new 19 leafs are passively cooled, I don't think Nissan will ever learn.
You don't want a 11-12 battery for the reasons that LeftieBiker stated. It's going to wear out very very fast. Also, I had one Nissan EV Help line person tell me that they can't release the refurb packs in the US due to EPA rules, and another rep say "they're working on making them available in the US" Who knows what the reality is and when, if ever, the refurb packs will be available.
You basically have three "good" options:
1) Buy a 13(April+)-15 battery, 24kWH. Open up both packs and swap the cells. Just swap the battery cells--don't try to swap the packs or BMS or cabling or anything. There is some risk that the new battery has been damaged or worn out, but that's pretty unlikely as long as you get a pack from a car in a colder climate and April '13 or newer. This is your cheapest option, but it is a full day's worth of work and you will need the proper equipment (HV gloves, etc).
2) Buy a new battery from Nissan. This will come with the factory warranty and Nissan will do all the work for you. It will run you around $8500.
3) Wait for Fenix Power to release their product. Keep in mind they're a new startup so the risk of failure is high.viewtopic.php?f=27&t=26597&start=70
4) Sell the car
I really wish there was a better option, and I'm as unhappy as you that Nissan raised the battery price. I bought my car expecting to pay $5500 in a year for a new battery, and they raised the price the next month. I'm also unhappy that Nissan won't install a higher capacity battery pack if I'm buying a whole new one, but unfortunately, that is today's reality.