combatcarl

I can see how having an alternator running at less than peak efficiency could affect a lot of things, including at least to a small extent, fuel mileage, even. But I'd agree that at 10.5 volts, your battery won't live long, you'll have starting issues, running issues, etc. as scope said, I get my best economy at about 58-64 mph. Running about 25-2700 rpm.
The drafting behind large vehicles can be a little unsafe, ymmv. I do it on occasion, but I've been around trucks and drivers most of my life, and really try not to be rude about it. A CB can help there.
I've had a rectifier fail. Killed my 12 yr old superawesomenumberone battery. Thing was fantastic, pissed me off.
But, the alt replacement worked for the OP, so it's all good. Something to consider if you're having general running issues, or are trying to hypermile a 20+ year old truck.

abecedarian

My brother has gone through at least a few "superawesomenumberone" batteries with a good alternator. Yellow and Red top's, if I remember correctly.


Me, I never go for the tip-top, high CCA ones- they always fail me within a year.


I tend to go for the more "RV" / deep cycle ones, and the last one is still going strong 6 years later... and often sees discharge to the 9-10v range.
I like to play the stereo, when working in the garage.

combatcarl

Well, it weren't anything that cool. Wish I had cash for one for a dual batt setup. It was a battery that was in it when we bought it in 97. Still goin strong. I was trying to set a record. But the I got the no start once or twice, then started to run like doodoo. Tested batt/alt, said batt over/ripple charged the battery and killed it.

mct75

I still maintain that a normal car battery would be reduced to sludge if used at 10V for any length of time. While "10 volts" can probably run the vehicle, a battery at 10 volts is going to be so shot that the voltage will drop to nothing the instant a starter motor hits it. I've killed a lot of car batteries in my time!

A normal "high CCA" battery is absolutely killed by being deep discharged. I think we all know that if you leave your headlights on overnight, you'll need a new battery soon. Marine/deep cycle batteries are more tolerant to this. They use thicker plates that resist sulfation better, but deliver less current. The CCA batteries have a honeycomb shaped plate with more surface area(more current), but they sulfate and disintegrate much easier.

I always prefer a deep cycle battery unless you have a giant motor or super high compression. I'd rather crank slowly for a minute than quickly for a few seconds!