stannah 300?

my stairlift stops every couple of inches on the way up an not on the way down. to get it to go up i have to switch off at the arm and on again to reset it then the up position to go furter on the other arm then it stops again. i have not got the battery charger conected and the stairlift has not been in use for two years. it worked fine for 4 ups and downs and then started with this fault.is it the charger not being connected or will it be the main pcb?