superbrain 977

Hi i just got my superbrain 977, i cant seem to get it to charge. I plug in the battery and then press start and it straight away says its finished charging, But when i press stop it doesnt work, it just keeps beeping telling me its finished and i cant stop it unless i pull the battery out. When i pull the battery out it just turns off even though its still connected to the powersupply. Then i have to unplug it and leave it for 10 secs then plug it back in and it turns on. It can discharge fine, its just charging thats the problem.

I live in New Zealand so im using a current converter cause our ac output is 240v,the current converter turns it into 110v. I looked on the charger and it says input is 120v-240v so is the 110v the problem? the current converter is made specifically for american plugs so i thought it should work. I might try hooking it up the the car battery and see if it does the same thing.

I just tried charging it again and it did it again so i pulled out the plug and it still was going beep beep.... for ages, so i pulled out the batteries.

any ideas?