How to roll start a w115

[JordaanDMC-12]

Okay this may be a taboo topic? I don't know, I have a feeling it's very much frowned upon....

Any who I went up last night with my friend to the high desert to go in the pretty cold 29 degree weather and get a hot chocolate! So we go up and There was a good portion of the drive where I had to use my highbeams. Now I've had battery charging issues but assumed they were fixed when I replaced the voltage regulator because I wasn't having issues like I was before. But I noticed the lights were dimming and was like "crap" lol

I had one of those jumpers that you hook up the car to and start it with so I wasn't worried. We stopped and got some hot coco and chilled and came back and the car was dead, no biggie i'll jump it. So I go to jump it and it drains my jumper and we're just left there. lol So we decided to roll start it, well we push it up this little hill and rolled it down at approx 13-15 mph and tried to roll start it in first and second gear and it would not turn on.... I was puzzled because it was relatively easy on this BMW we had long ago and my friends BMW and on this beetle we detailed awhile back that had starter problems. But of course it was my car that had to be the rebel and just not want to start by roll starting.

So my question is, how do you properly roll start this car to get it to start?(For emergency situations) Which gear? What Speed? cause what we were doing was not working. We tried it four times and gave up because it was heavy and damn cold outside, I admitted defeat and called AAA and got a replacement battery and we were on our way home.