11.9 is very marginal
New battery's properly charged start out between 12.6 and 13
When I was at this level (12 ish)on my old battery I got long cranks
before it would start . If I drove it on the high way awhile I could
get it up to 12.4 but it would be back down to under 12 while sitting
If you look at the pictures in the above DIY the glass eye is in the center of the battery its also obscured by the hold down piece and the battery distribution block a little . If you look you will see three dots yellow , green and black that the eye is more or less inline with those and half obscured by the black battery distribution block (which is also red on some cars) but you can see it without taking anything off if you look at the right angle.