What about lithium batteries? I am helping with 2 EV conversions using this battery chemistry. One conversion is using batteries from Headway. (HW) The other from Thundersky. (TS) The difference is the Watt-Hour capacity and the $$.

In order to compare apples and apples, I will try to compare similar packs - lead and lithium. My EV is capable of 55 miles, fully discharged. I have 8,892 watt hours in usable energy in the batteries.

There are 2 factors when building a battery pack: 1). Assembling for range, and 2). assembling for voltage. For example, my car needs 156 volts, and my truck needs 228 volts. In the case of the Headway batteries, the watt hours per cell is low, and to get the range (Watt-hours) the pack is a series - parallel combination of cells. For the Thundersky batteries, there are multiple amp-hour capacities available. The pack will be a series combination.

The Tesla has 6800 cells, in a massive series-parallel combination. The range is 230 miles per charge.

For lithium packs, I have heard that the number of charge cycles is 2000 for 80% discharge , and 3000 for 70% discharge. I want a pack, with normal use, that will give me 3000 charge cycles. For my 30 mile commute, I use 220 watt-hours per mile, of 30 * 220 = 6600 watt-hours. I want this to be 70% discharged, so the pack needs to be 30% more, or 6600 * 1.3 = 8580 watt-hours.

The number of cells in series for 156 volt pack lithium is TS: 156 / 3.5 = 52.

Target watt-hours 8,580.

Cell voltage: 3.5

Charge cycles 3000. Years = 3000/365 = 8.2 years

Energy per cell: HW: 36 w-hr. TS60: 210 w-hr TS90: 315 w-hr.

Cells to get the watt hours: HW: 8,580 / 36 = 238. But since this pack will be a series parallel combo, the cell count needs to be a multiple of 52. (5 x 52 =) 260 or (6 x 52 =) 312 ; I will choose 5 parallel. Cell count is 260.

Cells to get the watt hours: TS60: 8,580/210 = 40... TS90: 8,580 / 260 = 33. But I need 52 to get the voltage.

Cell cost: HW: $17 TS60: $66 TS90: $99

Pack Cost: HW: $4420 TS60: $3432 TS90: $5148

Balancer cost: $300. This is wishful thinking on my part. But maybe, when I go to lithium, this price will be in the ballpark.

Total cost: HW: $4720 , TS60: $3732 TS90: $5448

--------------------------------------Summary-------Lithium is a clear winner over lead acid cells.----------------------------------

Miles per pack charge: HW: = 42. TS60 = 49. TS 90 = 74.

$ / year: HW:$575/YR, TS60: $455/YR, TS90: $664/YR Lead Acid Gel Cells: $1138/YR.

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The $/yr for Headway compared to Thundersky is about equal. Another option that I may use in my truck, is flooded lead cells. The cost is about 1/2 of the gel cells. If the life is greater than 50% of the gel's, then it is a winner. Except, I have to water the cells, and provide ventilation for the hydrogen out-gassing. More $.

For evaluating the ROI, or payback, ckick here.

The other advantage of using lithium, is that the weight is 1/2 that of lead acid batteries. This reduced weight should translate to fewer watt-hours per mile.