Ok here’s my deal, when I first start my car in the morning my battery voltage reads 13.90-14.00 up and down. As the day goes on it will start to get lower and lower. By the end of the day when I get home it is usually around 11.90-12.30. Why does it decay like that?

F.Y.I

New alt.
New Batt.

mine does that too!!!!!! tonight i was just sitting with a cd playing and my volts were down around 12. they were up around 15 this morning.

Voltage is regulated in part by engine temperature. Hotter engine = less voltage.

^Yup, and since the stock voltage regulator is 11.5 volts, your reading seem normal at least at idle. Once you are moving and the engine is turning your voltage should be higher in the 13 to 14 volt range.



15.9 @ 86.7mph
97 Eclipse RS

Injen CAI, 55mm TB, P&P Intake, Crower Stage 2 Cams, Hooker Header, GS-T Muffler, AFX UDP, Crane Ign Amp, S-AFC

so... is it that the battery gets hot and lowers the voltage or that the alternator gets hot.. mine does this and its become rather annoying since my lights dim at idle now.. and they didnt use to. Battery is 2yrs old.. not the stock one.. i know that the afx udp doesnt help much, but it would be nice to have a higher voltage at idle at times.. neways.. im sure there may not be a lot i can do about this for cheap.. like i cant afford a alternator rebuild or whatever or even afford a new beefier battery, but the battery is easier to do then the alternator..

bah.. im just rambling now.. :)