Building hub motor bike, which batteries?

The price for those SLA batteries you've found is very low.

The key is that 12ah of SLA is not really 12ah.
You'll get 10-15 miles or so depending on temperature and how fast you go. If you drain the SLA often, you'll be replacing them often as they don't tolerate that well.

LifePo4 you can almost abuse (from what I have read). Completely drain, leave uncharged, etc. Doesn't give a darn about temperature. And you'll really get the 10ah out of it. Also, I think your $500 price is high? 36V 10AH LifePo4 from pingping is $400 shipped. Though you are going to want more than 10ah from what I have read if you do hills alot as the draw rate is too low and you'll get cut off. It's not recommended to parallel LifePo4.

I have to use SLA because I can't afford anything else, but if I had the money I'd use LifePo4 for certain. Far less hassle, far more reliable.

added: oh and 36v 10ah LifePo4 is only 8 pounds, 11x4.5x3 inches

The real answer to your question lies in how far you want to go. Depending on how fast you drain them, lead batteries can give you a whole lot less than the rated capacity. To get it all you have to ride real slow. Also you get a lot less life out of lead if you can't charge frequently. If you ride to work, and can't plug in, you will wear out the pack quicker. For me, the max range of 12ah lead was about 6 to 8 miles with a brushed hub. But I allways ride full throttle. Since I needed to climb a hill for 12 miles to get home, I never made it all the way till I got a large lifepo4. If the money is no problem, get lifepo4. You'll love the lightness and the extra range. My 20ah weighs 15 lbs, so a 10 may only weigh about 8 pounds. But if you are going less than 6 miles per charging opportunity, lead batteries will work excellent. Just don't leave em uncharged any longer than you have to.

Mines a Ping, boy am I glad I bought when I did. There is a new seller on ebay today, but some of the other sellers batterys weren't as well assembled as pings. If you have the money, the yesa's are considered by many to be higher quality than pings. Nowdays the best lifepo4 is the one you can get your greedy hands on.

This is speculation of course but I suspect after the olympics that LifePo4 availability will definitely go up as China allows factories resume full power (and pollution). Also shipping costs will go down because they cannot ship via EMS right now and have to use UPS because of "security".

(olympics end August 24th)

I just wish I could afford LifePo4.
I'm still figuring if I can make a NiMH pack out of sub-c batteries somehow for less than $200.

I know the feeling, I have the battery, but still need to pay the bill! I suspect that a year from now I will feel like a fool for the price I paid, but this summer, many will pay more than I did.

I'm still figuring if I can make a NiMH pack out of sub-c batteries somehow for less than $200.

Don't do it. Small cells in NiCd and NiMh don't like the amperage the motor requires. You will kill you battery real fast. The smallest you can do with is D or better yet M cell.

You can get a 37v LiOn pack of 9Ah for about $230: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2447

And after first month or so and losing 15 pounds you can add another 4.4Ah :)

Don't do it. Small cells in NiCd and NiMh don't like the amperage the motor requires. You will kill you battery real fast.

They will handle more current than the Li-ion you posted, and without similar risk of fire or explosion. I would be extremely wary of using Li-ion cobalt cells. The pack you linked can only handle 8.4 amps.

Sub C NiMh or NiCad cells can handle about 15-30 amps continuous, and the impedance at 1 khz is similar or even lower than the D chinese cells. If you go with high quality cells, such as Sanyo, or SAFT, than the D cell impedance will probably be lower.

Where can you buy 30 12aH D-cell NiMH for $180?