[Jay2oh]

So I was on the drive with the 416 ticking over as the battery went flat, and the Mrs said when the car was running she was getting interference on her
phone watching youtube videos.
Not sure if it's related but the battery will last a week tops on the drive before flat, and the voltage is at 12.33 fully charged.
Battery date is June 22. any thoughts ?

[g259fsg]

The battery is relatively new and the voltage is good, although I've had batteries that don't last as long as they should. The interference is odd, but could come from ignition. Must be something draining it when it's standing. Try putting an ammeter in series with one of the battery leads to see what it is. If it's 100 mA or more that will eventually discharge the battery. The other thing to check is the alternator. Check there is no current going through the alternator connection to the battery when the engine is switched off. Don't leave it connected when you start the engine or it will blow up the ammeter! There should be no current on this lead with the engine off, but if the rectifier assembly in the alternator is faulty, some current can be drawn. Assume the alternator warning light goes off when you start the engine.

[Jay2oh]

Yeah battery light goes off fine. Thanks I'll try testing with the meter and see what's happening, just thought it was strange with the interference as I've never experienced that before, but
saying that its been many moons since I've had a car with a distributor.

[g259fsg]

I did have an occasion 10 years ago when the battery wasn't getting enough charge from the alternator and eventually went flat. In this case the alternator was working well enough to turn off the alternator warning light but was only delivering about 10 amps, not enough to keep things going. That was a rectifier fault. Worth checking your alternator is doing the business. With the engine running, and nothing switched on, the voltage at the battery should be 14V +/- 0.2 to 0.3V. Switch on the headlights, and it will drop a bit but would normally be above 13V. That shows the alternator is supplying all the demand.

Hugh

[Jay2oh]

Thanks for that I didn't think to check it with load on too.

[Jay2oh]

Just an update, it was the bulb in the boot staying on that caused the battery dying on me

[g259fsg]

That's interesting, as I've had exactly the same problem on a couple of occasions. It's easy to leave the boot not fully closed. Unlike the other courtesy lights, this one isn't on a timer, just a simple on/off switch and will flatten the battery in a couple of days. After the last flat battery, I changed the boot bulb to LED with much lower current drain.

[Jay2oh]

It was very hot as soon as I opened the boot which I'm guessing was the culprit as since disconnecting it's been fine, just need to eat more carrots now