pramac 5kVA question

[harryspark]

hi guys, i work for a generator company and we have around 8 sets of small 5kVA single phase pramac generators, brand new out of the package they have a 110v, 0v and 230v switch, when in 230v it gives 230v and then when you switch back to 0v it gives a reading of 15v on the multimeter. does anyone know why, i have tried my other meter and another generator and it is still bringing the same result. it is just out of interest what yo guys thing would be the reason they make them like that?

p.s it is not the battery voltage is it? may be a stupid question but they use a 12v battery