Thanks for the good info, looks like 12 cell is best
I see the 6 cell battery has a 61 Wh rating vs the 12 cell has a 98 Wh one, so that would seem to mean the 12 cell one would last just over 1.5 times longer per charge. I gather from your comments that both 6 and 12 cell one have a 300 cycle life, right? I see it also weighs 1.3 lb vs .8 lb, so it's about 1/2 lb heavier. That's no big deal for me, but might be for some.
What about buying a battery from a creditable computer store. The local store where I bought this laptop has been in business there for over 24 years and is part of a national chain. Could I make a significant saving without much of a risk by buying from this store instead of Toshiba?