"my 2005 dodge spinter 3500 2.7 diesel has bat light on that says hi whats this mean?

Means output is to high this can be casued by low battery water bad regulator a loose wire on the altanator or starter and would need to be tested to know for sure, However most auto parts stores will test the ouput for you and give you an ideal. The only thing is if you have it tested post the results here so we can give a detailed way to test your issure. I could answer this with more information but the test voltage and amperage output would give me enoght information to keep you from spending money on parts and a lot of tests at the auto parts store.
If you leave it like this it could damage your electrical system. Hope this helps and thanks for using fix-ya!