Battery powered PC?

[#1]

You are getting your cranking current confused with your Ampere-hours there Mr. Shutter.
The reference to heavy-duty in relation to vehicle batteries is an attempt to indicate more ability to deliver short bursts of high current (aka the cranking current) to turn a starter motor. Ampere-hours is a measure of ability to deliver sustained current over a long period of time, and as such, any two batteries with the same Ampere-hour rating should deliver about the amount of energy over the same period of time and same operating conditions, (always assuming that the same standards and methods are used in calculate the Ampere-hour value, of course - there are different standards for it in different industries!).
In my earlier post, I should perhaps have mentioned that using the Ampere-hour rating in the way I did is a bit dodgy. The A-h rating is measured under standardised conditions, and as such is handy for comparing batteries from different manufacturers, but is a rather poor indication of performance in the real world. The real A-h rating of a battery depends on operating conditions and can vary considerably. It might be worthwhile for Sprite to do a practical test with a fully charged battery, a car light bulb and some meters, to see how long a battery would last with say, a 20, 40, and 60 watt continuous load. There is a possibility that the results will be better than I have suggested. But, as Mr. A Fox is Evil wrote, trickle charging from another power source is probably going to be necessary.

[#2]

Quite possibly    but I was trying to point out the difference between battery types... i.e. as you, and I, rightly said,... Heavy Duty refers to the cranking current required to turn the starter motor & engine, rather than being like a Heavy Duty torch battery which is designed to be used for a long time...

[#3]

Hi all,
Some interesting points raised here most of which I'd managed to come up with myself but needed to hear it from elsewhere.
So, I'm between a rock and a hard place. Its looking like mini itx or laptop hardware will be too heavy for a car battery to last any serious amount of time. I can't get any mains power at the location so even a miniITX board is looking like its a no-no. The raspberry thing looks semi interesting but its a linux only thing from what I could make out from a quick scan-read of the page and I've no idea where to start with programming for a linux system. I basically need to operate a door lock, monitor some PIR sensors (while logging time and date of any activity) and to activate a camera / webcam.
I've looked at some of the leisure batteries but even those are out of the price range.
Ok, another angle of attack, I can reach the site by wireless, so anyone know of a USB transceiver that offers two way communication? - I'd need it to interact with a USB device at the site (a USB control board), As long as there is a USB connection I can still do this!

[#4]

have you considered a battery pack with solar cell, not cheap for the cells big enough to keep it charged..
Maplin do a range, some on sale at the moment  http://www.maplin.co.uk/13w-solar-briefcase-99760?ordercode=N00CX&C=Email-Newsletter&U=12P2-2-N00CX&...

[#5]

Try Googling "GSM video remote lock" I came up with several devices such as this one. A bit pricey, but a possible avenue of investigation?

[#6]

Yikes, the price!! The camera actually needs to go somewhere else on the site so that wouldn't work for me anyway.
I suppose the best way for me to describe the site is an allotment with a shed with another piece of land the other side of the fence which we're responsible for. It's the shed and that other piece of land I am looking at protecting. Shed with a small system that can monitor / log / record activity and the camera monitoring the other piece of land connected to the shed system.
If there was a mains outlet there this would be a piece of cake as I've got loads of old systems that could be used via the mains but unfortunately thats not possible

[#7]

I am using a sheevaplug and a dreamplug as my servers at home. They consume less than 5W at the plug end and run debian squeeze. If you open them up and take out the power supply then you can run them from 5V (If I remember correctly). Some people have run them from solar panels. The cost about £100.

[#8]

If you have a telephone line, they may supply you with enough current?
May be illegal though.

[#9]

There are also a number of very useful low power arm based linux computers available. What you are asking it to do doesn't require a very powerful computer, For example, my dreamplug serves music while running a web server, database server and e-mail server, it also monitors PIRs in my house and is used to turn on and off devices in the house. It also integrates with the security system.
Have you looked at gumstix (google gumstix), there are also embedded arm computers (google embeddedarm). You should be able to get down to about 2W. This will make providing a power source much easier.

[#10]

Cheap wind turbine: http://www.instructables.com/id/A-Paper-Plate-and-Pop-Bottle-Savonius-Wind-Turbine/