WRT previous answers, I have the following to add.

I have been operating my laptop from this powerpack for nearly 2 hours and it is still going. The power supply for the laptop is rated at 240V / 2A, which would equal 580 watts, although I would imagine that it actually draws much less than this. With a 20Ah battery, in theory, this should power a 2A device for 10 hours.

Further, the 2.5A rating on your plug may refer to the fuse and not the actual power draw (I believe I read somewhere that my laptop actually runs at 190 watts or about 0.8A).

It is possible that it would power your appliance, but not if it really draws 2.5A

No, not this one.
Amps x Volts = Watts
2.5 x 250 = 625 Watts
Inverter supplying 230 volts is only rated at 300 Watts and it does not state if this is Peak Power, ie for a short period or Continuous power level.

These devices are not meant to power anything that requires great Wattage for heating like Hairdryers. Every hairdryer I have looked at requires between 1500 and 2000 Watts power.
The device could power your hairdryer on blow cold only but what is the point.
These devices are for running low wattage equipment like LAPTOPS or SMALL TV's or charging your mobile.
If you require high Wattage when away from a mains electricity supply you will have to buy a petrol generator capable of supplying 2000 Watts and they cost anything from£600 to £1000.

Please contact the Helpline for this product 0113 2137339 and they will be able to order a new mains adapter for you.

Please contact the Helpline for this product 0113 2137339 and they will be able to order a new mains adapter for you.

This is correct your battery is fully charged. The green and amber lights will go out as your battery level decreases, leaving you only with the red 'warning' light to show that the battery is almost empty.

I've used it to jump start a motorbike. Not tried using it to charge though but seems powerful enough.

take your car to a dealer they can change your valve for you it doesnt normally cost much

Based on a 20AH battey, theroetically you should have a 5 hour running time given that you are drawing 4A so I would expect a good 4 hours from a fully charged and good condition battery. Perhapes Halfords could clarify further how they expect 3 Hours?

Thanks, Andy

But is it normal for the fan to be running constantly? I'd expect it to come on and switch off as needed.