Ok chaps first post here and I need your help. I've had a recurring battery problem that has come to a head now and needs to be resolved. It's costing me a fortune getting taxis to work and back.
My 1999 535i had the original battery for around eight years before it died and I replaced it with another BMW-sourced battery. That one died just outside warranty (1 year I think). I replaced the second battery with a non-BMW one and now that has just died on me after one year. So, I can accept one bad-egg battery (the second BMW one), but two? No, too much of a coincidence; something is killing my bats!
Current problem sequence of events: Over past couple of weeks car seems barely perceptibly sluggish to fire up (normally practically instant). I didn't do anything about it. After much snow and some days of no use, go to start and “click, click, click”. I fully charge the battery and the car starts; the next morning I go to drive to work and although it turns over, seems not enough to start it.
So I measured some voltages:
Fully charged the battery yields 12.4V across its terminals open-circuit which, temperature-adjusted to 0C, seems to me to be fully charged.
With a cold engine running I measure the alternator output voltage (at the battery terminals):
Engine idling: 13.95V
More than idle: 14.00V
Engine idling under load (lights, heater fan): 13.75V
Engine more than idle under load: 13.80V
After (nervously!) driving around doing errands for a couple of hours (leaving the engine running), we have a nice warm engine and, presumably, fully charged battery. The alternator outputs:
Engine idling: 13.35 – 13.70V (fluctuating)
More than idle: couldn't measure / no voltage measured!***
Engine idling under load (lights, heater fan): 12.52V
Engine more than idle under load: couldn't measure / no voltage measured!***
*** Despite attempting to measure the voltage across the battery terminals in the normal way, couldn't find a reading. Battery definitely HAD a voltage as it had just started the engine no probs. Tried various different points on terminals but nothing at all. It has always been hard to get a voltage measurement from the battery/alternator. Sometimes it's no problem, can put the probes anywhere on the terminals/connector braces to get reading. Other times you have to hunt for a reading.
I've not yet measured the current drain when all locked up and 'asleep'.
Apologies for the epic post, I know this crops up a lot having googled it, but I've come to the end of my diagnostic abilities and would be grateful of help.
Thanks in advance.