Well, you also have to consider practicality... If I know my physics, lol, the electrovaya battery, which is supposed to be incredible with its charge ability and lasts 6 hours with a normal lappy, will only hold up for 2 hours on the 8886.... This laptop is a BEAST. lol, putting a second battery in that modular bay will prolly mean using the one the 5660 uses, and that means you will prolly get half an hour more... Personally, I don't think it would be worth putting extra wiring in there for that. That's my opinion though. I can see where every little minute helps.