Batteries & alternators

[carlo]

Could anyone guide me with a little problem. I went out and bought a new battery from Halfords today as the one in my 405 was discharging every two to three days if I didn't use it.When I hooked it up tonight it was totally dead (the new one). It just about started with a jump, and having used the car then for ten miles and tried to start it again it was virtually dead again.Does this point to an alternator problem, or does the fact that the new one was dead when I put it in indicate the new battery could be faulty?

[marinast]

Slow discharging like this could be down to something silly like an internal light staying on, does the car have a working boot light? If so then try to gain access to it from inside and see if the light stays on with the boot closed.You can check the alternator by starting the engine and connecting a multimeter to an earth and then to the positive battery side, select the meter to DC current and you should get a reading of between 12.5 to 14.5 volts, anything under 12 volts could point to a weak alternator. Also check the drive belt as sometimes a loose belt can be the problem and they don't always screech like a banshee when slack!Hope this helps.

[Dead_E23]

Erm - you might want to set that meter to the DC voltage scale!

[carlo]

Thanks for those guys. I'm still a bit surprised though that a brand new battery doesn't fire straight away - is that normal?

[pogweasel]

No, it must have a fairly major drain on it. My old BMW used to have permanantly illuminated window switches (no idea why) and that would take a very long time to drain down to non-starting. Is it the 'right' battery for the application?My touring had a piddly piece of crud when I got it that just wouldn't hold charge, have since swapped for a big hefty proper one, nay bother since

[Timewaster]

The new battery should have a decent charge in it off the shelf and should have started the car regardless of any power drain or fooked alternator on the car.This would still apply even if it was the wrong battery for the car.Back to Hellfords in the morning methinks.Incidently - if you want the right battery for the 405 it should be an 027 or possibly an 075 on a diseasel, 065 on a petrol.Hope that helps!

[carlo]

Cheers Tontops, that's what I thought.

[M'coli]

There is another option, the earth from the engine to the body might be poor. It can happen suddenly.Easiest test for this is to connect a jump lead or similar to the engine and then to a body earthpoint or straight onto the battery.

[Pete-M]

No, it must have a fairly major drain on it. My old BMW used to have permanantly illuminated window switches (no idea why) and that would take a very long time to drain down to non-starting. Is it the 'right' battery for the application?My touring had a piddly piece of crud when I got it that just wouldn't hold charge, have since swapped for a big hefty proper one, nay bother since

The switches were illuminated because one of the front door courtesy light switches was earthed - they've got two connections on the front door ones, one to trigger the electric windows / sunroof when the front door is open, the other does the actual interior light. Very often people remove the switch and don't realise they have two wires.

[pogweasel]

Sounds likely, Pete-M.Gotta love the electrics on these old things, I've had the NSR window pack up almost completely today. Goes down fine, goes back up in 5mm increments. JOY.