I read a lot of websites to find the best way to cut the lightening holes in the battery box. Most people have used fly cutters or hole saws. Well, following what worked for others, I started out by using a metal cutting hole saw. I thought it was going to work fine when it began cutting thru the powdercoating. That ended quickly when the teeth hit the stainless steel. After an hour went by, I had two holes VERY roughly cut, and a ruined hole saw. I began the third hole with that hole saw, and then switched to my fly cutter. I must have a cheap fly cutter or something, because that only lasted about 20 minutes before it was junk. I ended up sawing thru that third hole with a box cutter (the SS was pretty thin). At that point, I became rather frustrated with the whole thing, and quit.
This is the crappy result-
Today, I found the solution...and the TIP to pass along! Greenlee punches (if you have them, or access to them...they are expensive!) I also highly recommend a hydraulically actuated punch piston, but that's a bit over the top for a home tool. Our avionics shop has a whole set of Greenlee punches, AND the hydraulic actuator! This was SO FREAKIN' EASY that I could kick myself for not thinking of this last night!
Here's the setup...
The punch sliced thru the SS like a hot knife on a stick of butter...the hole on the left was just done-
At the end of the day, I had ALL the holes done, and the other NINE holes took a total of 20 minutes!! Now, it would take a bit longer without the hydraulic actuator, but using a socket or wrench with the punch would be dramatically faster.
I did put lightening holes in the sides of the box, which is not in the plans, but I saw the sides of the box as being HEAVY, so I put cut 'em out!
I just found this tool SO COOL, that I had to share it! 
