Hi people.....please please help,

I've had a major problem with my Walkera Devo F7 in terms of charging. Firstly I had no idea Walkera didn't even supply a charger after ages of trying to find one. Then I bought a Prophet Sport LiPo charger and tried plugging the 800mah 15c battery to it....again the Prophet doesn't even think there is a battery there when it's plugged in and won't charge it. Is it the battery or the Prophet Sport Pro?

I should mention the battery hasn't been charged in a while.