Posted: 02/12/2013 at 11:13
I'd love someone to prove me wrong here, as it would be a great solution for me too, but when I looked into it last year I came to the conclusion it would be immensely impractical.
You would need at least two leisure batteries, one in use, one on charge, and you would have to swap them at least every two days but if you timed it wrong and drained the battery completely you would kill it dead and that would be really expensive. Even for two days worth of charge you are barely looking at move than a basic frost-killing setting on a 12v heater. I doubt you'd even notice it working unless you stood right over it.
I then tried a little butane gas cylinder camping heater but it was uneconomical and only created a warm area of about three foot diameter and I move around a lot more than that in my shed.
I ended up opting for an Aladdin paraffin heater for my shed because I have good ventilation and I buy paraffin for the GH heaters so it's no bother but if I didn't mind lugging the cylinder back and forth for refil I would have opted for a calor-gas heater as being the most cost-effective and safest option.