I would actually be very surprised if they only lasted for 500 cycles. Apple currently says their devices last 1000 cycles and Tesla is very careful with their

I would actually be very surprised if they only lasted for 500 cycles. Apple currently says their devices last 1000 cycles and Tesla is very careful with their batteries. They recommend not charging it below and above a certain percentage in their cars and it would surprise me if it was any different in their battery packs (though I believe they do not have such an option -- they just do it automatically). Furthermore, those packs have dedicated cooling and a low discharge rate, and are made for a lot of discharges (unlike iphones, which are made to be purchased every two to four years). According to Wikipedia[0], the original Powerwall was rated for 1000-1500 cycles and it would suprise me if Tesla's new powerwalls are not better. So, they should be even cheaper then your estimate, especially when you consider that they will probably be used well after the 20% capacity lose. [0]: https://en.wikipedia.org/wiki/Tesla_Powerwall#cite_ref-te2015-05-06_11-0 https://en.wikipedia.org/wiki/Tesla_Powerwall#cite_ref-te201...