13.8 Volts at idle,is it normal ?

yep, thats dead on!

Yep, bang on.  The constancy tells you your battery is probably in good shape too.  Remember though, voltage is not the best indicator of alternator condition. An amp probe and carbon pile will tell you more.  Stay away from transistorized battery testers,  sometimes older technology is better.

My dual batt diesel runs at 14.5.  Depending on make and model, you can see anywhere from 13.5 to 14.8 Volts.  More than that and you risk damage to the battery.  If you only see 12.5 or something, your charging system has a problem.Chris

14.8 is the perfect amount of volt's for a system. most amp's are desighned and tested at 14.8 . 13.8 is good better then some. but if you want to get the most out of you're amps 14.8 is the way to go.Thomas

14.8 is the perfect amount of volt's for a system. most amp's are desighned and tested at 14.8 . 13.8 is good better then some. but if you want to get the most out of you're amps 14.8 is the way to go.Thomas

actually as many designers of top brands such as jbl, jl and etc they have said that top volts for there tests are 13.5 due to the fact that most people dont use caps or special altenators  so they dont want there product the cause of a malfunction. even the top amps are tested low volltage. think about it the less voltage needed the more the car can reproduce power to supply the equipment. Jon

Installer/Help Technician

---coral springs florida---

mecp certification is not always needed. I have it and it has not helped me out at all. my experience out shines it.

most brands actually like ma audio, volfenhag, xtant, and soundstream all test and desighn at 14.8... so i guess i stand corrected some desighn at 14.8 and some don't like jbl and jl audio.Thomas

lower brand amps test there stuff at high voltage so they can advertise a higher output. upper name brands test at lower, more constant voltage and put out even more when the voltage is up above what they were  tested at.