Advice On Flat Battery

[Prudie]

What instrument would you suggest is needed to determine what is draining a car battery flat if car left standing a week. Battery has been checked as fine so something is draining it. What would you do to fault diagnose? Obvious things such as boot light left on etc etc eliminated. Happens every time I go away.

[Zacs-Master]

Could be your alternator that’s not doing it’s job. Halfords do a free check, I think.

[Zacs-Master]

Sorry, superfluous apostrophe in its.

[Metaphysicalus]

It might be a defective alternator diode. It will cause the circuit to charge even when the engine is shut off. At least, that is what was causing the problem that I once had with a draining batter.

[TonyV]

If you want to try and diagnose yourself I would use a multi-meter so that volts,amps, and ohms can be checked at various locations ~ something like this
https://www.ebay.co.uk/itm/1-Digital-Multimeter-Ohm-Voltmeter-Ammeter-AVO-Meter-DT830D-Test-Leads-Black-/183113680670
If you don,t feel comfortable using something like this, I would let a local auto electrician check it out, shouldn't cost to much to diagnose fault. If you can ask if you know anyone who could recommend one to you.

[Metaphysicalus]

Battery I mean - not a fish and chips dilemma.

[Prudie]

Things OH might have in garage (like voltmeter/ammeter or something or other) could they help? If it was a faulty alternator would I not get a warning light plus sluggish start on Monday mornings after a weekend rest if it wasn't charging properly?

[Zacs-Master]

Yes, the battery light (red square with + and -) should show with a faulty alternator but it won’t if the battery is flat. Obvs. I don’t really think there’s anything that you could check it with which would give a meaningful reading

[vulcan42]

Just a thought, a friend of mine had the same problem. After a couple of trips to the garage and finding no fault, on the third visit a bright young mechanic found it after touching the bulb in the glove compartment and realised it was far too hot for being on the normal few seconds. The bulb was on all the time and the switch was found to be faulty.

[Prudie]

That's interesting Vulcan and one to try but more concerning is it raises the fact that it could be a myriad of things, the alarm is another one that's been mentioned to me.

[goodgoalie]

Prudie, check that nothing like a radio or internal light of some kind is left on - the most common reason for a battery running down. Useful advice here:
https://www.honestjohn.co.uk/forum/post/119556/sz2---suzuki-swift