PC1100 Battery Post Repair

My favorite F3b winch battery is an Odyssey Extreeme PC1100.   It's only drawback is the weird choice of M6 studs for the battery termination.  I have been using some battery posts I machined for a few years, but I did have one of them where the stud broke.  I might have over tightened it.

The Swiss team mentioned they had broken one and used a Helicoil to repair the battery.  I called up Odyssey and they didn't think there was any way to drill it or enough material there.  But looking at it, there clearly is a bit of lead/copper before you get down into the cell.  I picked up an M6 helicoil kit. 

The only problem is the tap was for a through hole. It isn't a bottoming tap.  So I ground off the end of the tip to make it closer to a bottoming tap.   I tried drilling a piece of lead to see how deep I needed to drill and how well it worked.   It looks like I could get away with 1/2 inch.   The M6 set requires a ,250 hole to tap.  

I mounted the battery in the vice on the milling machine and got out a 1/4 mill  I  figured a flat bottom would be best to get the depth needed. I was able to go down 9/16 without any problem on the negative terminal that I was repairing.

The helicoil installed nicely.  I picked up a M6 bolt on battery terminal and trimmed the bolt to make sure it would be just the right length through the helicoil.   Everything looks fine.    I have a usable battery now.

Odyssey started making SAE Terminal Kits for the 6mm. This is a relatively new addition.  I will be switching to these on the other batteries.