I have a 1996 VW Passat Estate 1.9TD the battery goes flat after a day or 2 running. With a fully charged battery in it it shows 12.5volts when ticking over.when a go to start the carthe dash lighs come on as normal(shown the batterys no totally dead) on the 3rd turn o the key u can here a ckicking sound from the dash and the clock and miles counter reset. av concluded ma self that the alternator aint doing its job as there no charge going to batery when the cars being driven but someones also suggested the starter motor ??? any help will be much appreciated cheers ta for now

After checking for loose connections, I would replace the cable coming from the alternator to the battery. Before changing the cable, drive the car for some time so that the battery is fully charged. Leave it disconnected for overnight. Connect it in the morning and see how strong the battery is in starting the car. If it turns the motor fast, that means the cable has short. You can order new one from dealer or get the part number and do goole to find a seller. I had similar problem in my 2002 Jetta TDI. I replaced the starter and the cable to solve the problem for ever.

If the alternator is bad the light should come on & stay on. Bad, loose, & or corroded bat wires will inhibit charging bat. Make shure all connections are clean & tight, i disconnect bat & take off connections, wire brush them clean, apply dialectric grease, reattach them making shure their tight. I had a wire come out of its terminal y-day. Bad crimp frm factory. Also, wires that look good can be terribly corroded under the outter sheath. Dont forget to clean whatever metal the ground wires hook to. If this dosent help check bat for cold cranking amps. Even tho it may read over 12 volts it may not have the amps to constantly start it. Much luck to u.

Hi:
A fully charged battery should read approx 12.6 volts. When you check the voltage of a running vehicle, it should read approx 14.5 volts or so. If it doesn't, you are not going to charge. You are most likely driving around with a junk alternator, and if it has a bad regulator, it will discharge your battery. Most auto shops will test alternators for free!