invertors are very inaficent they use more power than they chuck out so a car or liesure battery wont last long maybe less than 2 hours depending on the consumption of the incy. i went to an auction and got one of those 60s/70s grey cabinet parifin incys as a back up, you can get them on ebay sometimes, look out for one as a backup. theres one on ebay now its 10 mile from me might bid, i paid £14 for mine, ebay number 220570380681