Lithium a better performance per $ than lead?

Sorry about the sloppy looking original post.  I had the epiphany, but I didn't have much time to explain myself.  The main point to take away is this:

If you buy a 100AH lead acid battery and want it to last, you'll only use 30AH (30% Dod).  That will get you around 3000 charge-discharge cycles.

However, with a 100AH LiFePO4 (lithium iron phosphate) battery you can use 80AH (80% DoD) of its capacity and still be left with 3000 cycles.  In case you ran it to 70% DoD you would get 5000 cycles.

So, even though the lithium batteries are more expensive for the same rated AH, you actually get a lot more usable capacity with LiFePO4.

Now, add the fact that lead acid batteries can only reach their rated AH capacity if you discharge them at no more than a 1/20 C rate and you watch your real world capacity diminish further.  LiFePO4 generally are rated between 2.5C and 3C, giving them much greater overhead and efficiency.  Take this example:

A 12V, 100AH lead acid battery has an ideal usable capacity (30% DoD) of 360 watt hours, at a discharge rate of 60 watts (1/20C).

a 12.8V, 100AH lithium iron phosphate battery has an ideal usable capacity (80% DoD) of 1,024 watt hours, at a discharge rate of 3,840 watts (3C).

After taking into account the DoD of these two chemistries, lead acid comes in at around $0.60 per watt-hour, and LiFePO4 comes in at around $0.57 per watt-hour.

Other advantages of LiFePO4:
-Operating temperature of up to 85ºC, rather than lead's 60ºC
-Truly a sealed, maintenance-free, non-toxic, and non-spillable paste
-No worry about plate thickness or corrosion

The only thing we would need are solar charge controllers and inverters designed for lithium iron phosphate.  That is, a charger with a goal of 3.7V per cell (3.2V nominal), and an inverter with a low voltage disconnect of 2.7V per cell.

Alan, I think we are close. LiFePo4 (lfp) are great, but they do have their shortfalls as well. They work great hot, but not as well as lead acid in cold temperatures. A lead acid cell, kept properly charged will live for years and years. Lithium batteries of any type begin to degrade the moment they are manufactured. LFP also have some of the worst c/rate of the lithiums. c rate is more of a determing factor for longevity on lfp than DoD. Their c rate may be equal to or worse than that of lead acid.
If your packs were big enough this may be acceptable for a solar system. For a scooter, just the reduction in weight would surly be worth it. I have a 36v, 12ah battery bank on my ride, and it weighs around 65lbs. Sucks.
Just like solar, the problem with lithium isn't it's particular ups or down, it's the up front cost.
A company by the name of Axion Power is supposedly developing a "light" lead acid. It will be interesting to see if it happens, but i'm not holding my breath... -m