Whats the use of using a laptop if cannot take it anywhere with you, for me the main idea of purchasing and using a laptop is so that I would be able to surf the net, check my online messages and do some work while being on the road or in a cafe while waiting for someone or just killing some time.
1) Your laptop is 15- 17" big and weighs like 3-4 kilos having big screens and footprint therefore not much space on the table for your coffee
2) Big screens have more power consumption and is much more likely to get knocked on by a clumsy passer by
3) You dont need a big laptop for presentations (theres a projector for that)
4) using a 3-4cell battery means that It wouldn't last very long, Short lasting batteries means that you would have to search for a power outlet and thus have to make room for the charger adapter to kept in the bag aswell
The key factors for getting a portable and stamina laptops
1) the smaller the screen the less power required to light it up. 10" screens might sacrifice keyboard size so 12"-13.3" screens are the way to go. 15" above... a big NO NO!!
2) if possible get a laptop that has at least a 6cell battery.. 9 cells would be better
3)ULV processor are good too coz ULV means Ultra Low Voltage (although sacrifices performance)
4) Dont leave CDs or DVDs inside the drive if you are not using it
5) lastly get one that doesn't use a fan to cool the processor but uses the conductivity of heatsinks and alloy casings. Not having a fan would dramatically increase your laptops battery life 2 folds. One such laptop is the fujitsu P7120 battery can go 6 hours!!