Portable Pwr for MBP ?

Greetings
I look for a portable, chargeable device (battery) that can recharge my Mac Book Pro when in the field. I guess I should also know how many amps (?) is required for each charge of the MBP so I may realize the capacity of the device I select. I see nothing from Apple for such use.
Thanks In Advance

I would look at these units:
http://www.hypershop.com/HyperJuice/Ext ... Phone-USB/

Pretty pricey $350 includes a kit to modify your magsafe so doesn't work out of the box unless you pay another $100 to have them do it...... If you want a cheaper solution look into a car charger:

http://www.ebay.com.au/bhp/macbook-pro-car-charger

and then get a 12V battery, a few options around, a sealed lead acid is pretty cheap but heavy, add a Cigarette lighter socket on leads and you are set or look at the options here:

http://www.megabatteries.com/cat_featur ... 1&uid=1318

You will also need a charger to recharge the 12V battery.

As far as battery capacity goes a quick google shows macbook pro batteries are about 65 W-hr or 10.9V and 5500 mA-hr. So a 7 A-hr sealed lead acid would give a full charge more or less. What will work will depend on what you mean by in the field. If you are carrying it on your back the sealed lead acid will be an issue. As an alternative to that you can now get 12V Li based batteries like this:

http://www.batteriesdirect.com.au/shop/ ... 2-7.5.html

12V 7.5 A-hr and 1 kg, but $165 in Aus, comapred to about $30-$40 for a sealed lead acid.

I use my laptop a lot out in the field and I keep it charged via the cigarette lighter socket in the car. 12V chargers are readily available in most stores that carry that type of product. It takes about 40 kilometres of slow driving in the bush to fully charge my laptop so it is no big deal. My fridge freezer and often my camera battery are charging at the same time too.

I watch TV at night on my laptop plus review my images and for that I have a 120 Amp hour power pack with cigarette sockets plus an inverter if I need it to run the laptop as required. I usually plug the laptop into the powerpack to review the images as it works a lot quicker on a power source, then just use the laptop battery to view the news and weather on the laptop.

I can stay off grid for 8-10 days with laptop, fridge and lights with the battery and trickle feeding the batteries via the car as I drive around.

Thanks all for the helpful information.
I have a device that plugs into the lighter port of my truck, creates 110v spike-less power and can charge the MBP... I want to avoid the situation of having to run the truck only to get a charge...because I know I will if pressed and it seems somewhat ridiculous (I will be in places where the photo ops I want are only accessible by foot / no daily driving around).
So...looks like a power pack. It will permit me to do the digital stitching / stacking before I leave the area to see what happened...and what didn't.
Cool Beans

If you have a truck then you could get a product like this one that I have. It works very well and I can charge it via solar panel if I am not driving around so you have plenty of power day and night to charge other batteries, run the lap top or lights and it will power a winch if required. I have a separate battery for my fridge but my powerpack acts as a back up if it goes flat.

http://www.arkcorp.com.au/p/3231/arkpak-715