Hi, hooked up the battery in my New To Me 04 Islandia to test the lights and stereo. Turned the key and fuel gauge went up so I assumed I was good to go. Turned on various lights for about 5-10 minutes. All of a sudden I hear a long loud beep and the low battery warning system switch is lit up? I pushed the button and the beep stopped but the light stayed lit. I removed the battery and took it to an auto place and it tested fine. Any ideas what the problem is?