Do I have a flat battery?

garethgas

Hello, I wonder if anyone can offer me some advice?
My Audi's battery is running flat after 3 or 4 days of not being used. I've checked the voltage (12.88 v) and removed the neg and am getting a zero reading when testing amps. When the engine is running I'm getting over 14 v
The battery is only 16 months old and this problem was there when I bought it but I used it a lot more then so it wasn't really an issue although I keep it trickle charged during the week in case I get stranded.
Any ideas of where to go from here?

s_b

a proper battery test would confirm or deny
it doesnt help that you are constantly trickling it
be aware a battery tester person might be looking to sell you a battery so best go to a garage small that you can trust

garethgas

Thanks for that. Now I'm doubly confused lol.
First, I would expect at least a few mA to be trickling out when everything was normal but I'm getting 0.00A.
Second, I thought that it was good practice to keep a battery fully charged. (I use a CTEK)
Am I wrong here?

waynedance

Cars that don't get used tend to eat batteries.

Work at a garage and most battery changes on not very old cars are low usage ones. My 12 year old car with 140k has the original battery, clutch and exhaust.

forgotmyname

12.8 after charging but what voltage after its been standing all night and what voltage under a load?

Leave overnight, Put all your lights on for 10 minutes and check the voltage, with the lights still on.

Do this without starting the car though.

Voltage under load could be much lower, Especially if a cell is dodgy.

Cars batteries need to be fully charged as much as possible, Flat battery will kill the cells.

Notmyrealname

What kind of journeys are you doing? If they're short journeys, you'll not be replacing the charge used to start the car.

garethgas

forgotmyname wrote: »

12.8 after charging but what voltage after its been standing all night and what voltage under a load?

Leave overnight, Put all your lights on for 10 minutes and check the voltage, with the lights still on.

Do this without starting the car though.

Voltage under load could be much lower, Especially if a cell is dodgy.

Cars batteries need to be fully charged as much as possible, Flat battery will kill the cells.

OK. I checked voltage this morning after battery disconnected overnight. 12.88v last night 12.84 this morning.
Headlights and heater blower on on for 10 mins then 11.4v.
Started engine and got 14.4v
I suspect that SB's suggestion would be the best place to start really but I feel that there is more to this than a faulty battery (its still under warranty).
The reason for this is that the previous owner obviously had a problem for him to change it in the first place (a few weeks before I bought the car) and its all too easy to just fit a new one without investigating the root cause.
Also, when the battery was 2 months old I noticed that it wasn't holding its charge so I suspect it was mis diagnosed at that time.
This is the reason I'm reluctant to assume its the battery (Bosch 75AH) and more likely to be something else.
Any ideas/suggestions would be very welcome.

marlot

You really need to get the battery drop tested (where they place a 100A load across it and measure the voltage drop). This is best done when its fully charged. That would eliminate the battery.

Your trickle charger could be faulty (I had a battery wrecked by one that was).

It could be the diode pack in the alternator. Or a bad connection - eg. some rust around the earth strap, or a missing damaged strap from the car body to earth.

marlot

garethgas wrote: »

Thanks for that. Now I'm doubly confused lol.
First, I would expect at least a few mA to be trickling out when everything was normal but I'm getting 0.00A.
Second, I thought that it was good practice to keep a battery fully charged. (I use a CTEK)
Am I wrong here?

I agree. 0mA is unlikely. Makes me wonder about a bad earth. Try putting a jump lead from the earth to a decent spot on the engine and see if it changes.

Yes, lead acid batteries are best kept fully charged.

garethgas

marlot wrote: »

I agree. 0mA is unlikely. Makes me wonder about a bad earth. Try putting a jump lead from the earth to a decent spot on the engine and see if it changes.

Yes, lead acid batteries are best kept fully charged.

That's a blinking flip good idea!
I will do that tonight.
Thank you to everyone with your suggestions :beer: