Presumably you've checked that your alternator is actually charging the battery, as form first impressions from what you describe this is where I'd be looking first.
I wouldn't return the earth cable to the chassis from the transfer box, I'd add another. (one going to chassis directly, one going to transfer box.
Argghh, die grinder swarf, sharp little buggers get everywhere...
I've just bought a 90 degree 1/4" die grinder as I've always found you can never quite get the inline ones in where you want to.
Typically though, I havn't found a use for it now I've got it. lol
Andy