Battery dies after a day?

  • CS111's Avatar
    I've got a 2005 2lr automatic golf that I bought last year second hand. When I first purchased it the battery lasted on avg 3 days, meaning if I didn't drive it for three days it would die. I'm a new driver and didn't use it as much as I thought I would last year. I ended up changing the battery anyway because a family member told me to, even though the battery looked new.

    That battery was fine for a few weeks but then it started doing the same. Now the battery dies after one day. I can use it Monday, leave it till tuesday evening & its dead. I usually use it every other day and it gets driven for about a hour, though I usually take a few detours if I've got time so it's running longer in an attempt to keep the battery charged, makes no difference. A family member drove it aswell for a few hours after jump starting it and it's the same outcome.

    Nothing looks corroded or obviously broken. It's been through a mot this year, no issues and had a full check when I first bought it.

    But I've also got a leak somewhere as the drivers side carpet & the seat directly behind get soaked if I leave the car uncovered in the rain. It has a sunroof but I'm not sure it's coming from there because there's no wet patches around it.(or anywhere else, I've checked a hundred times), + the screen above the steering wheel goes on/off which I think is probably water damage.

    So I'm asking if anyone knows what this could be and if the leak could be related. Thanks.
  • 2 Replies

  • Best Answer

    NMNeil's Avatar
    Best Answer
    As it's a new battery it's unlikely that it's bad, not a 100% guarantee but unlikely.
    Common causes are a constant but smallish battery drain, such as the light in the glovebox staying on, but from experience the most likely cause is a bad alternator.
    I don't know how handy you are with spanners, or in this case with electrics, but if you have a multimeter put it across the battery terminals with the car running, it should show between 13.8 and 14.6 volts DC. If it's well over that you have a bad regulator inside the alternator and it's overcharging and frying the battery. Now switch the meter to read AC and if the reading is more than about 300mV, then you have bad diodes inside the alternator.
    I don't know how much electrical knowledge you have but the diodes are one way valves and the generated voltage from the alternator will only go one way, into the battery, a bad diode will let the voltage go the other way, through the field coils and to ground, discharging the battery.
  • CS111's Avatar
    @NMNeil Thanks for the reply. I will give this a go this week.