Hi there,,,,,its going to be the main carriage batteries,,[though first check to see that the spur mains supply to the white charger has not been turned off by mistake]if there is no fault found there then your looking at replacing the 2 x 12 volt 7.2 amp batteries,these only last between 3 to 5 years depending on wear and tear of stair lift.you can test the ones in your stair lift with a meter and if the combined volts fall below 22 volts then you will need new batteries,,also the first signs of batteries faulting are the stair lift stopping going up but will come down ok......hope this helps.........paul...portsmouth
paul, January 2014