My portable battery pack smells like copper, can I continue using it?

I have a Powersource Mobile Mini, I got it as a gift years ago from a techie who said he got a bunch of them cheap due to a defect so it has me a little worried now that is has started smelling like copper. I would be worried regardless, they are quite large batteries and it’s years old. It’s highly reliable and takes forever to die though, but if this thing explodes or leaks it’s big enough to do some damage. What should I do? I assume the fumes are bad too.