Black and Decker drill 18v li-ion battery not charging?

Hi, the battery in my drill went dead so obviously charged it used it the next day and it went flat almost straigh away so put in back on charge again and no lights come on the charger at all, I'd have thought the fuse would be blown but you cant get into the plug at all, one of the new moulded plugs. Ive checked the battery on a volt meter and its showing between 14 and 15v and a repair specialist told me that if its showing any less than the 18v displayed then one of the cells have gone, but surely a light would still register on the charger as it has pictures of a fully charged battery with green light, charging battery with blinking green light, broken battery with blinking red light and temperature with intermittent blinking red???

Please help
Thanks
Bobby