Now, before you have to spend 45 minutes with a battery charger after you are finished... you might miss a good time playing pool with your friends.
Diesels have 2 batteries for a reason. That reason is not so you can ignore one of them.
This is a public service announcement.
i think im in the same mode tonight...
I have to remember to hook my car (the one in storage) up to the trickle charger--it's been awhile--probably dead. 
Yeah had the same issue. Battery showed good power, but she would not turn over. Turned out to be build up on the posts.
Wire brushed them clean and presto.
What not to do, is flick yourself in the eye with a tiny bit of battery terminal muck while going nuts with the wire brush.
Or accidentally get a lungfull of that crystallized blue stuff. It burns!
BG makes an awesome terminal cleaner. We use it here at the dealership. Spray it on, it disolves all that corrosion and then there's a red coating you spray on there to keep it from returning. Did it to my P71 YEARS ago when I worked at Firestone in Austin, still haven't seen a bit of corrosion on there.
Rinse
Pour Baking Soda or Coca Cola onto terminals
Wait a few minutes
Rinse
Done if its a POS - dry with a disposal rag if not
