I rebuilt a 4 year old worn out 3000mAh 15.6V (13 cell) NiMH Battery pack with higher capacity 3800mAh tabbed cells after finding that the least expensive replacement pack was ~$90 with shipping. I purchased the tabbed cells from an eBay store for 1/2 the price. They have all types and sizes of cells.
eBay Store - All-Battery Center: Battery Charger Kits, 8.4V, Nimh Nicd Batteries
I'm an electronics technician and it took me 4 hours to take apart the old pack and rebuild it. You have to be so careful not to accidentally short out any cells. I drew an arc once while soldering 2 cells together when the soldering iron touched something it shouldn't have. I used a small piece of mylar to keep from melting the plastic directly below the tab areas.