[david mark]

Have One of my vans parked on street.need to keep it warm over night.On EBay there's a 150 watt fan heater runs on 12 volts if wired up to a 140 amp leisure battery could this keep the van warm for around 8 hours,and hopefully stop everything from freezing. up.

[slap bash]

WAtts are not amp hours. You would have to see how many amps it draws. But I have never seen a heater work on a battery for long time and produce heat. I would guess its a no. But get a second opinion.

[Window Lickers]

Not a chance.