s.f.w. said:
The only thing like that, would be an external battery pack, that sits or clips underneath the notebook. They usually connect via an AC/DC combo adapter. They were taken off the market, as they were heavy, got extremely hot, and were relatively expensive.
Depending on the age of your notebook, even a 9 cell or 12 cell battery may only last 3-4 hours.
If you can post or PM me the part number or model number of your notebook, I'll see what I can find out for you.