Battery discharging

on my 2000 330d it was the (original) bmw phone charger that discharged sometimes the battery... took years to identify the cause...:( it was very quick, in one hour you couldnt start the engine, but the accessories still worked... good luck ! you will need it...

Can I suggest looking in the usual places first, Boot/trunk lamp, glove box light, under hood lamp if fitted.

Simple test is to connect an ammeter in line with the battery feed (DO NOT TRY AND START THE ENGINE) and see the drain with nothing on then open the trunk/boot and see if the load increases (note if the lamp is on) then open the doors, glove box etc.

Note if any changes take place to increase the load or decrease it. Eventually switch everything off and there should be a very minute current drain that would normally keep the radio memory and or other memory functions ticking over but anything nearing 1 amp drain is too much. Finally remove all bulbs that you cannot see - glove box and trunk/hood or even the torch charger cigarette lighter seat warmer seat sensors and belt sensors etc.

Probably best to get the quiescent spec from a dealer first to see what it should be.

then there is the sublimely obvious - the diodes in the alternator. These can and often leak back to ground if faulty and it's very difficult to know as they will allow the battery to charge and of course discharge.

A good auto electrician can check the diode pack for you.

No need to use a pro to check - simply disconnect the alternator output if you see a high quiescent current, say around 3 amps. But wait for several minutes for the car electrics to go to sleep, depending on model, to get a true reading. If it then goes to a low figure of under

BTW, it's often best when inserting an ammeter - if a DVM - to wire a bit of scrap wire in parallel and wait a few minutes. Then remove the wire leaving the DVM in circuit. The reason for this - the switch on surge may blow the meter fuse if fitted or even the meter itself.

If, "over a year ago," you bought a 24 month battery, you could be approaching end life of the battery you have.

Put an ammeter in series with the battery. Note the discharge... if it is more than 10mA or so, you have a worry. Start pulling fuses out and see which circuit the draw is on. If all the fuses are out and there is still current drawn, disconnect the alternator. Once you have located which circuit the parasitic load is on, you can start checking each thing on that circuit.

--scott

Only if it's an original BMW one. Others usually last much longer. ;-)

The life of a battery is price dependent. If one buys a cheap battery, they will get short life. Batteries come in a variety of life spans, longer life spans command higher prices. I once bought a pair of el-cheapo 36 month batteries for my motorhome, and they died in the 37th month, I swear to God.

On the other hand, I had an Optima battery in my Jeep that lasted more than

Then BMW must fit the cheapest - mine died just days outside the three year warrenty. So suddenly I reckon they have a built in time bomb. ;-)

I had problems getting an exact replacement for my 528 - my local large motor factor didn't have one - and neither did my branch of Eurocarparts. But they pointed me at the Bosch dealer on the same estate. Who had one which was identical in every way to the BMW one - apart from the badge. That's now 6 years old and still fine. It cost what I'd expect for a reasonable make - I don't by cheapies.

There's lasting and lasting. Optima set great store about how long their batteries last - but don't put their money where their mouth is with a warrenty.

The original battery is still doing fine, in my 2000 323i...