Right here we go. I've checked the wicki about this problem but cannot find exactly the same issue there.
Over the last month or so my main battery discharges quickly. It is just a year old, and there has not been a problem before and I have not added or changed anything electrical since. The regulator is charging fine. After a short journey the battery is back to about 12.6V and the starter motor restarts perfectly. The charge is now dropping by about 0.3 volts over night. Assuming that the engine/gearbox earth straps are fine, Is this possibly an earth crown problem behind the fusebox? I'm asking cos I have never understood how vehicle electrics work (some kind of mysterious magic?)and this problem is a pain. Cheers.
Patrick
You can't measure battery voltage immediately after charging, it will be artifically high, you need to wait a few hours. If the volatage keeps dropping then it could be either somthing taking a load or a faulty battery.
start by removing the battery + strap and WITH EVERYTHING SWITCHED OFF connect a multimeter (check it's a 10A and set it in ammeter mode ) in series, first to the smaller wire (most of the vehicle electrics), then repeat with the large wire ( starter alternator and some engine electrics) this will tell you if something is drawing current, there may be a small current for clock and radio but it should not be much. If there is current on the smaller wire start pulling fuses and see which ones make a change. If there is current on the large wire then that is more worrying and may indicate a short.
Just to add, these symptoms are not connected with any earth straps.
As mentioned above, after a drive, leave it for around 2 hours and measure the voltage, it should be a minimum of 12.6 and preferably 12.8, any less indicates a failing battery. The charging voltage, engine running and after a bit of a run should read a minimum of 13.8 and preferably nearer to 14. (some modern regulators go as high as 14.5 volts).
If doing the current (Amps) draw test as above ^^^ you often get up to 100 milliamps consumption (radio and clock etc). Any higher indicates something is drawing current when it shouldn't. Take care when doing these current tests if you are not experienced with electrics, as mentioned you need a test meter with at least a 5 Amp range and these are not quite so common. It is VERY easy to blow your meter if you make a mistake with current drain testing.
My guess, in view of what you say = the battery is on it's way out.
Has it ever been run down until it is pretty much flat ?
Cheers guys. I think that my multimeter can cope on ammeter side.
No mate the battery has never been left to run down. It stood still for a month back in October/November when having the hailstone damage repaired at the coachworks, but started without a problem and I drive it regularly. The battery was new from a reputable battery provider in March last year, so I doubt that is the problem but it's possible I suppose.
I'll go and check things out in an hour or so. Cheers again.
I have followed instructions. Disconnected + battery terminal and connected the ammeter to the thick cable in line, no discharge. I then connected the two small cables also connected on the + side. No discharge from one, but I have found a 0.05 discharge on the other one. Back out to check the fuse side of this to try and find out what is casuing this.
I had a similar prob with mine - seems this cold snap has damaged my battery
Took it back to Halfrauds and they swapped it no bothers - it was a Bosch...
They are normally the first thing I change to on a new car, its seems even they are becoming lower quality
Single cab pickup, running 1996 Subaru WRX STI engine, Aiden talbot gearbox.
Right when I checked again with an assistant, I got a measurement of .10A, which is quite a lot I think. Checked all the fuses and the offending fuse was No 7. As soon as I took that one out the meter went back to .05A. Trouble is my Haynes manual only refers to fuses 1-5 on my early bullet type fuse box so I will go back after my hot x bun and tea and see what is not working when that 16A fuse is taken out.
Fuse 7 does not seem to affect any of the normal functions eg lights, wipers, stereo, engine, fridge etc. So I will leave this fuse out for now and see what happens. If this continues to be a problem I will have to try something else. Thanks again guys.
Fin wrote:I had a similar prob with mine - seems this cold snap has damaged my battery
Took it back to Halfrauds and they swapped it no bothers - it was a Bosch...
They are normally the first thing I change to on a new car, its seems even they are becoming lower quality
Mine's a Varta battery. I will check the battery over the next few days. I am taking the van on a proper run tomorrow. If it's still a problem in a few days I may well take the battery back for replacement as you did. Cheers.
Ralf85 wrote:Fuse 7 does not seem to affect any of the normal functions.
Fuse 7 on the early fuse box is listed as "spare" on the famous Brickyard chart here > LINKY
Cheers. I'm intigued as to what is connected to fuse 7. It's like a ball of spaghetti behind the fuse box. There is definitely a drain on fuse 7. Battery now showing 12.5V having rested for several hours after driving. I will put it on charge on Thursday to see what that does to improve the voltage.
By the way this message chain has really helped me and probably lots of others to understand more about the mysteries of car batteries and the way they work. Thank you guys.
Last edited by Ralf85 on 04 Apr 2013, 11:45, edited 1 time in total.
