BATTERY GOES DEAD CAR NEEDS JUMP
Battery constantly goes dead, even after it was replaced.....do the simple tests on it before you spend big bucks having a shop pin down the problem....you will need needle nose pliers, 20 volt dc scale volt/ohms meter, test light 12v, battery charger 12v,bright flash light.
Ok lets get this party started, first have the battery charged over night if on a slow trickle, keep the battery cables off overnight, next put the volt meter on it black neg...red pos. set to 20 dcvolt scale, statically the battery shoukld read 12.5 volts anything less it needs to be replaced, next.. reinstall the cables and start the car...what is your reading...12.5 volts???? this is straight battery voltage and indicates that the alternator/regulator combo is not charging... cause may be a broken wire off the back of the alternator or a bad alternator, possibly a stretched and loose alt. belt.
If wires look ok and the belt tests tight(with engine off try to turn the alternator pulley by hand, if it turns the belt is way too loose or defective..tighten or replace)..then suspect the alternator/regulator...remove it and take it to Discount Auto or Auto Zone there they will bench test it for output if no good replace it.
Ok if your reading was 13.0-14.5 the alt/reg is charging, turn on all electrical is the reading on the dv volt scale at about 12.8-13.0 volts, this is fine...now shut all accesories off and it should go to full charge 14.5..all good....anything less have the alt/reg bench tested as stated above.
Ok everythibng seems to be in charging order but it still goes dead...you have a direct drain on your electrical system knocking the daylights out of your battery, ok first disconnect every mercury under hood and trunk light you find and let it sit overnight(also go around the car in the dark and see if any lights are lit such as a bad brake light switch illuminating the brake lights while you sleep thus draining the battery overnight) next morning does it start...yes then replace the mercury lights and be certain they are adjusted perfectly because they cant be seen if they come on under the hood or trunk, Ok all that and still no find...take the positive cable off the battery and in series with it install your 12v test light...needle pin in the cable alligator clip on the post or vice versa....you are now testing for a draw in the system that may be killing your battery while sitting over night,
go to the under dash fuse panel and one fuse at a time remove it... each time while it is removed check to see if the test light is on or off...it will go off when you find the circuit that the drain is in, mark the fuse in the panel when you find it and see if you can visually observe any wiring problems in that particular circuit(have a manual handy to locate which fuse controls what circuit in the fuse panel) example if the cigar lighter fuse is pulled out and the test light goes out... look at the lighter element... we have found children who put pennies inside the cigar lighter element causing a horrible drain on the battery and very difficault to find as well.
Hope this helps in you diagnostic adventures of basic electrical 101.
on Aug 10, 2010 | BMW 323 Cars & Trucks