a trip to maplins in falkirk yesterday proved to be a waste of time. they only sell 24v stuff online. having thought about it though, most modern trucks have a 12v cigarette lighter rather than 24v so maybe a 24v charger wouldnt work anyway. would i be better off buying a 12v charger and only using it in a 12v socket? if so, which one do i need? they have different wattages but i cant find any wattage on my laptop. its a 19.5v/3.9A charger. input is 100v - 240v ~ 1.1A - 0.5A 50/60Hz.
advise please cos its been a long time since i sat my physics test and i am completely lost 
Watts = Volts * Amps 
With the figures you’ve got there, you’ll need 300W, although chances are you’d get away with less. My charger’s 240V/1.7A (408W) and works fine with a 350W through a lighter socket.
I’d stick with getting a 24v, not all motors have got 12v sockets, and the wiring on the 24’s are generally a lot beefier.
Another option if you just want it to charge a laptop, is a charger that plugs straight into a lighter socket. I got one from http://www.laptop-chargers.co.uk, it works perfect at 12 and 24 and it’s still going strong after 3 years use (It’s outlived 2 laptops so far). You can send them an e-mail with the make and model of the laptop, tell them you want it to run on 12 and 24, and they’ll pick out the right charger for you. It works out about the same price as an inverter, you get a spare charger out of it, and 24v → 19.5v makes a lot more sense than 24v → (12v ->) 240v → 19.5v. The only down side is different laptops have different charger sockets, and voltages, so if you replace the laptop, chances are you’ll need a new charger. (I’ve managed to get away with just bodging new plugs onto it so far, but it’s not something I’d recommend doing)
is it worth switching the plug to a hella plug if im going with 24v? i put up a thread a few weeks ago asking about a 24v kettle and although i am going for a gas cooker instead, someone did say that the hella socket is less prone to problems than the cigarette lighter socket.
im waiting to start a new job and the last thing i want to do is start off by burning out the electrics in their trucks. no kettles, no microwaves, no tvs but i would like my laptop to last more than 2 hours when im away from home 
I think hella sockets are designed for higher loads, so it’s better to go with them if you’ve got a choice, but for a 300W inverter I wouldn’t stress too much, the only lighter sockets I’ve had problems with is in the new XF (they seem to blow fuses if you look at them wrong).
Rather than changing the plug (which will void any warranties), you can go through something like this:
most services have got them for about a fiver, and it saves you doing what I did - ‘Right that’s the old plug off… err which wire was positive again?’ 
It’s unlikely you’ll burn anything out - that’s what the fuses are for, just have a quick look at the fuse box and make sure they’re all the right sizes in the right slots.
The fuses are matched to what the wiring can handle - if you’ve got a 5A wire with a 5A fuse and try to put 10A through it, the fuse blows and breaks the circuit, but if the fuse is 15A, it’ll happily let a 10A load through, but the wire can’t take that much, so the excess converts from electrical energy to heat energy as an escape route (like a light bulb, the glow is the wire (filament) getting extremely hot) - handy if your night heater doesn’t work, not so good if you’re allergic to fire
(that’s not technically accurate, but it’s close enough to explain why there’s smoke coming from your dashboard )
you had to say it. the fleet consists primarily of
an adapter could be my first purchase then
cheers mate 
Sods law innit?
Give it a try, like I say, as long as the fuses are right to begin with, the worst that can happen is a blown fuse - it’s a new motor, so there should be a set of spares.
All the XFs I’ve tried before have been 95s at the same company, so it could be they’ve specced them on the cheap. I had a 105 last night and that was fine with a 350W.