Laptop battery liftime from Dell specs?

Question: When I buy a Dell Laptop, I get the following choice for battery:
(Lithium-Ion main battery with X cells and Y Wh [included in price/at additional \$]

• Lithium-Ionen-Hauptakku mit 4 Zellen und 24 Wh [Im Preis enthalten]
• Lithium-Ionen-Hauptakku mit 9 Zellen und 85 Wh [zuzgl. CHF 120.01]
• Lithium-Ionen-Hauptakku mit 6 Zellen und 46 Wh [zuzgl. CHF 30.00
• I figured that I can calculate that a 86 Wh offers +254% of the 24 Wh lifetime, but...
Is there any way to calculate to what battery time this amounts in hours ?
I mean how many hours will the 24 Wh last (at normal operation - eg. writing a document - not watching video), else the +254% is a pretty useless number...
Also anybody knows whether 4 cells means 4 times 24 Wh, or 24 Wh in total?

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Depends on what you're using the laptop for. The more intense your experience, the more you can fizz pop. – random Jan 30 '10 at 12:23
It will last longer than the next upgrade, for sure. – techaddict Oct 3 '14 at 3:36