Li-Ion Power Tool cells work great for RC!

[MetalMan]

Many of the RC helicopter guys have started a new revolution - using Li-Ion cells pulled from common power tool batteries. They are cheap, powerful, and best of all, SAFE. Although how safe is not yet known, but they are safer than LiPo cells. Here's a place where you can buy 5s packs:
http://www.toolsforless.com/product/7364.html (this one is for 2)
You can also buy the same cells in a 7s configuration from Milwaukee power tools (I don't have a link, but you can find them on Ebay).

Here are some individual cell specs:
-3000mah
-15C
-~99g each
-Capable of high C charge (helicopter guys are doing close to 3C!)
-Something near 3.7v nominal
-Work with common LiPo chargers (many guys are using the Thunder Power charger/balancer setup)
-Can be soldered together like NiMh cells
-About 26.5mm diameter and 70mm long

If your battery tray could be expanded width-wise (by a couple of millimeters), then a 4s1p (14.8v 3000mah) pack could be built into a stick format that would require only slightly more space than 6 NiMh cells, and weigh only as much as 6 NiMh cells!
Did you notice the price? You can get 5s 6000mah for only $133...

The only downside seems to be that these cells are a bit heavy compared to LiPo cells. But, I'm sure a lot of that weight can be attributed to the durable cylindrical casing. Just for reference, a Thunder Power 4s3p 6000mah @12C pack would weigh 360g, would be 50mm wide x 26mm tall x 128mm long (x2), and would cost $275. A 4s2p (14.8v, 6000mah) pack from these Li-Ion cells would weigh ~800g, would be 53mm wide x 27mm tall x 140mm long, and costs only $133, for which price you would get 2 extra cells.

I'm thinking that this will be my next battery purchase, but I'm not sure if I should make 2 2s2p packs and put them in series or if I should make 2 4s1p packs, and switch them out when one is drained.