I did some math and guess what, I came up with 1.6-2.3X cost difference if the full lifespan was increased by 3-4X. Why? Because of the higher price of the battery that would be required to do the same job at 40% battery 3, 60% battery 2, compared to 80% used from battery 1.
I used... http://www.pingbattery.com/

1; 48v 10Ah, $382. at 80% used can go 19.2 miles

2; 48v 15Ah, $533. at 60% used can go 21.6 miles.... 1.6 more battery #1 is required.

3; 48v 20Ah, $658. at 40% used can go 19.2 miles... 2.27 more battery #1 is required.

So, is that still worth all the time and effort, special charger, extra money up front? Just wondering.