i've been thinking of 2 ways to do this,
1# is i could get between 6 hours and 18 hours depending on how much space i need that day in my back pack, an easyer way to do it is take (my backpack if i lay it on its back is 12" x 15" of space i can use i can fit atleast 48 side by side 8 in each row x6 rows so for each layer i get about 6 hours of life for my labtop i'm going to get see below, and for each row tape each battery(8 in each row) in series(this means if you took a wire from the negative of that battery to the positive of the next battery so if we had just 2 D batterys that would make the voltage to 3 volt's in stead of 1.5 or in parallel which means take the positive from each battery and connect them together and the other side the negative connect them together, then you have your 2 sperate wires, + and - its the same voltage but more amps means it makes it last longer like if u put like 8 d or a or c or ect... in parallel, it would last about 8 times aslong as 1 battery at the same voltage.
So we need 8 in each row to = 12 volt for the lil car inverter that plugs in the cigarette lighter that i'm going to use, i have an adaptor that i can plug the plug from the inverter in or i can cut the wires to the plug and wire it to the battery, but seeing how i dont have enough money for a sperate inverter just to keep in my backpack i'll use the adaptor i have so i can use it in the car. make sure you have the wires connect right so you dont fry it. now i have 6 rows of 8 D batterys that i have in series, and connect the 2 wires comeing from the left and right side of each row, i am going to connect them in parallel for even more amps thus the 6 hours with-out useing the battery in the labtop. now for the 12 - 18 hours just add 1 more layer for the 12 or 2 more layers for the 18 hours, for a total of 3 layers, and for my other ideas i'll post them when i get my new aw laptop, but i seen a picture of the power brick thats comes with my labtop(i dident think it was that big but its huge compared to the one for this labtop,) so i think i will only get 1 layer in, but theres other compartments i can put more batterys in,
i was looking at D 9000mAh NiMH Battery at the site i was at was $17.75 per battery then i found a site that had them for about $11 - $12