Many years ago (I think about 1987) when I worked for a BMW dealer we were told to never jump a dead battery in one of the Bemmers because the jump could cause a spike that would take out a VERY expensive PCM. We ALWAYS disconnected and charged, never jumped.

 

If a voltage regulator is "set" for 14.3-14.5V,(they're not adjustable, the voltage is "built" into it) no matter how dead the battery is it's not going to go above that. You're not going to see 15 or 16V no matter how dead it is. And also, batteries DON'T "usually crap out quick", they only SEEM to. Most batteries decline slowly over about the last year and a half or more before they die. I load test all my batteries about every 3 month at least and you can always see the decline as the battery ages. I would say I have seen decline as long as 2-2+ years until the battery is down to about 12V or so before I replace it. Full charge new should be AT LEAST 12.6V and some used to be as high as 12.8V. By the time they reach 12.0 V, the ice you're skating on is getting a little thin. It's just that 12V batteries don't normally show the decline in starter speed the way 6V batteries did. You "think" they "just crap out",but that's rarely how it actually happens according to Mr. Tester, 1st. name Load.