BongEx,
I assume this is similar to your drill:
http://www.ozito.com.au/productinfo.aspx?prodid=OZLICHD18A
Note the battery spec: 1.3Ah 18V = 23.4Wh
Your Laptop Battery: 4.2Ah 10.8V = 47Wh
Assuming you could transfer the charge from both your drill batteries to your laptop battery with 100% efficiency, AND assuming the Ni-Cad drill batteries are still capable of holding 100% rated capacity, you would be able to charge your laptop battery to 99% once, completely draining both drill batteries. I would doubt that your drill batteries will hold more than 75% of their rated capacity, and you would be lucky to transfer the charge with 80% efficiency (combined battery heat losses & DC to DC charge controller losses), so:
46.8Wh * .75 * .8 = 31.59Wh => 28.08/47 =59.7%
That is, you would, under what I would consider the best of circumstances, be able to charge your laptop to 59.7% using your two drill batteries. More realistically you might expect to charge your laptop battery to 40% to 50% using both drill batteries.
Assuming this is worthwhile, I would suggest you find a "car charger" for your laptop and modify it to connect to your drill batteries. This is far and above the cheapest/safest alternative. Your laptop already has the most efficient charge controller you could hope to find for that battery pack already built into it.
Using the same process for your 3.7V 1.08Ah cell-phone battery:
3.7V * 1.08Ah = 3.996Wh ==> 46.8Wh / 3.996Wh = 11.7 Charges In theory, in reality:
46.8 * .75 * .8 => 28.08 / 3.996 = 7 Charges
Again, I would strongly suggest you simply buy a "Car Charger" designed for the battery you are attempting to charge. While these are not likely to be as efficient as the laptop charger, they are cheap and safe for your intended purpose.
The camera battery is similar to the cell-phone.
While charging batteries is not rocket science, and designing/building DC to DC charge controllers is not a huge undertaking, adequate care needs to be taken to prevent damage to the batteries being charged. This includes fairly intimate knowledge about each battery being charged. Damage may range from shortened battery life to catastrophic failure (Read: Exploding Battery). I would consider the risk/reward ratio of designing and building three charge controllers for 46.8W of power abysmal.
If you purchased a "car charger" for your camera, cell-phone and your laptop and added a 25W solar panel, you could likely keep all three batteries charged with as little as 4 hours of direct sunlight/day. A 25W solar panel in the US ranges from ~$100 to ~$250.
I am sorry if these solutions do not meet your needs/budget, but maintaining high-tech devices in remote locations is generally expensive. Renewable Energy is typically quoted from $4/W to $20/W, but is typically far and away cheaper/more practical than toting generators to remote locations. Purchasing spare batteries for short duration trips vs purchasing and carrying something like a solar panel depends a lot on the trip/location/budget. In any case, I cannot see the 46.8Wh capacity of your two drill batteries doing much more than charging your phone/camera batteries. The laptop will require a more robust solution.
Hope this helps,
Fish
