Battery Light Keeps Coming On on 2000 Ford Windstar

My husband left the lights on and drained the battery months ago. He had it jumped off, but after that, the battery light when driving goes off and on. I have had the alternator checked and it is putting out 13.9 and when they checked my battery, it was fine. I was told to disconnect the battery for 2 minutes. If that doesn't work, what next?

Asked by for the 2000 Ford Windstar
add water to the battery open the caps on it and add water its helps me every time
It's a sealed battery. Has no caps to open.