FAO: Derestrictor

FAO: Derestrictor

Author
Discussion

_deano

Original Poster:

7,408 posts

259 months

Saturday 28th October 2006
quotequote all
Der,
When you had an issue with your e39M5 and the flat battery, what was the problem?
Went to start the car tonight and the bugger had a flat battery!

The car is used everyday, so not a weekend toy, somewhat baffled. The only thing that i can think of is bad wiring somewhere; i've noticed that the centre brake light dies more often than it should (i've replaced that blub twice in the last 2 months)

thanks
DJ

StuB

6,695 posts

245 months

Sunday 29th October 2006
quotequote all
Could be a duff cell in the battery also.

seesure

1,197 posts

245 months

Sunday 29th October 2006
quotequote all
Odd, I had a flat battery last night as well, I hadn't used the car for 5 days and it was parked up in the garage. (But had left it in the summer for over 3 weeks with no problems). It wouldn't even start with the jump leads connected from the wife's car, all I got was a clicking sound....

All I can think was that the alarm had been triggering and run the battery flat. Anyway disconnected the battery and stuck it on the charger overnight and it started no problem this morning.

_deano

Original Poster:

7,408 posts

259 months

Sunday 29th October 2006
quotequote all
no alarms went off the other night, espically not mine (it's quite loud). It been fine all day today as i took it out for a long drive.
one thing that i can think of is that the last week even though i do a 50 mile round trip i don't push the car that hard (no more than 3K rpm) as there is no need for it (70mph is around 2.5K rpm) and with the heater, radio/sub, rear screen demister and lights on, could this flattern the battery?

vee

3,101 posts

240 months

Sunday 29th October 2006
quotequote all
_deano said:
could this flattern the battery?


Only if the alternator wasn't doing its job.
The test is to measure voltage across the battery while the car is running.
I had the following measurements which meant my alternator needed changing (only a 330 but principle should be the same)

Idle : 10.something
Idle with electical items on : 9.something

If the alternator was working as it should, the reading should have been in excess of 13v while running regardless of electrical load.
I don't think your trip, which was quite long, at low rpm would have been the problem unless the alternator wasn't working.