voicepro Posted June 27, 2016 Report Share Posted June 27, 2016 When I check the digital readout on my '98 DeVille, I don't know whether the battery is getting, say, a 13.8 volt charge...or 13.8 volts is the demand being made of the system at that moment. Or is it what the battery has available at that moment? Duh... Anyone know which it is? Would be helpful to know. Thanks. Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted June 27, 2016 Report Share Posted June 27, 2016 Yes. The battery is putting out 13.8 V given the load on the battery at the time. When the voltage exceeds 12v the battery is charging. I am interested to hear other opinions as well, so we'll see what replies you get! Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
BodybyFisher Posted June 27, 2016 Report Share Posted June 27, 2016 I just read the owners manual and they refer to it as 'battery voltage' and they call normal 11.5 to 15.5 volts. You will notice that right after start up, the indicator will be high in the 13 to 14.5 range as the alternator is charging the battery and providing current to drive the coils. Once you drive for a while the charging voltage will drop. This indicator is a good way to monitor the charging system's health. Summer heat causes the charging efficiency to drop off and you will notice lower charging rates at idle. Here is an interesting article on how heat causes demands on alternators http://www.electronics-cooling.com/2002/05/thermal-design-challenges-in-automotive-alternator-power-electronics/ Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
OldCadTech Posted June 27, 2016 Report Share Posted June 27, 2016 The reading (13.8V ) is an applied voltage at the battery. If the battery was discharged, such as playing the radio during retained accessory power and you were monitoring the display since start up you might see 14.3V or whatever but 13.8 tells me it is operating as designed. If it was 12V or less when the engine was running the generator is not charging the battery. Hope that makes sense THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!! Link to comment Share on other sites More sharing options...
OldCadTech Posted June 27, 2016 Report Share Posted June 27, 2016 As an example; my '02 Seville when I picked it up from the previous owner would not start and several attempts later the battery was getting pretty weak. When I finally got it running it was indicating 15.2V ... Now I have driven it about 300 miles and it indicates 13.6V all the time now. THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!! Link to comment Share on other sites More sharing options...
cdgrinci Posted June 28, 2016 Report Share Posted June 28, 2016 This is a normal function (of a lot of GM vehicles); voltage is monitored, and when a certain stasis (e.g., battery is at full charge), the alternator reduces charging effect (thus saving a little fuel and the battery to a certain extent). It is called EPM; electrical power management. Chuck '25 CT5, '04 Bravada........but still lusting for that '69 Z-28 Link to comment Share on other sites More sharing options...
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