If you are interested in finding laptop battery packs with high capacity cells on ebay, it helps to know that government regulations require that battery packs with more than 100wH of capacity need to be transported as hazardous materials. Needless to say, no manufacturer sells battery packs with more than 100wH capacity.
The 100wH limit places an upper bound on the number of cells in a pack, and their overall capacity.
In the past, companies sold 12 cell packs. Those packs might seem like a great source of cells, but keep in mind that the cells won’t have more than ~2,300 mAh nameplate capacity. Actual capacity could be even lower, because 12 cell packs are probably more than 5 years old.
Improved energy densities mean that extended packs are now more likely to have 9 cells. A 9 cell pack at the 100Wh limit will have cells with ~3,000-3,100mAh capacity.
If you want cells with more than 3,000 to 3,100 mAh capacity, you’ll have to look at 8 or 6 cell packs. The best cells 18650 available today have a capacity of 3,200-3,400mAh. An 8 cell pack with such cells would be in the 95-100wH range. A 6 cell pack with such cells would come in at ~75wH.
I haven’t come across any packs in this range, but I’m also focusing my attention on packs that work out to $2-3/cell, which pretty much rules out anything using the latest and greatest cell technology.
So, bottom line, if you are looking for 3,000 mAh cells, you need to confine your search to packs with 9 cells or fewer. If you are looking for 3,200-3,400 mAh cells, you’ll need to narrow your search further to packs with 8 cells or fewer. Happy hunting!