Battery drain, alternator etc

[Black_JPN]

Just got my car back from a bit of work and noticed over the weekend as I moved it around that it was getting harder and harder to start it. Until this lunchtime when it wouldn't go at all and I had to jump start it.

The battery is only 2 months old. The starter is newish (a year or so) and I can't detect any drain anywhere (lights, alarm, fans etc all bahaving normally).

Voltage at the battery terminals is just over 13V at idle with no electrics on and I can get it down to 11.70V with absolutely everything turned on (lights, fog lights, full beam, fan, air con, both wipers, heated window, fan, you name it). I'm thinking this isn't bad but still not brilliant as I'm sure I was getting 14V on the dial before with no electrics on. Battery voltage is 11.7V when completely unhooked.

I've unearthed the battery for tonight and will reconnect tomorrow, see if its charge has been lost but could the alternator be at fault? Were my readings normal

 

[DavidL]

I wouldn't have thought you should be able to get it under 12 on an external gauge.
It is possible you could be driving using all these things which would eventually drain the battery.
Alternator and voltage regulator would be a good place to start.

 

[zcacogp]

I had something fairly similar with my S2 about 4 months ago. Sluggish starting (and getting more so, with time, so I didn't really notice it.) Then it let me down when I had left the sidelights on for 4 hours or so one day. Very annoying.

Jump start got me going, but I noticed it was showing 11v when driving in daylight with no electrical load.

New alternator cured it.

A test to do - test the battery voltage with the engine off. Then start it and test the voltage again. You should see around 13.8v with the engine running, and at least 12 with it off. If there is little difference between the running voltage and the non-running voltage, it is probably an alternator up the spout.

You can change the regulator, but I was advised against this by a number of people - apparently it is nothing more than a short-term fix, and will cost more in the long run. BUT, beware - new alternators are eye-wateringly expensive. Some way north of £200, from memory.


Oli.