Battery or Altenator?

[BZG Wagon]

GF's '98 1500 Mazda Familia battery keeps going flat.

When the car is off I get 12.6v off the battery terminals.
When the car is running I get 13.90v off the battery terminals.
When the car is running with headlights etc on full & engine @ 2000rpm I get 14.0v off the battery terminals.

Or else a faulty starter motor? Is there any other test I can do? Is there a way to see how much current the alarm etc. is drawing when the car is off?

[Lloyd]

Going flat overnight I take it?

And are you checking battery voltage with it off quite soon after turning the engine off? Likely the 12.6V isn't an accurate reading if thats the case

Either way, sounds like battery

[BZG Wagon]

Going flat overnight I take it?

And are you checking battery voltage with it off quite soon after turning the engine off? Likely the 12.6V isn't an accurate reading if thats the case

Either way, sounds like battery

Nah; like after a few hours.

12.6v was taken about 15 mins after a decent drive.

Battery was taken from my 98' 3sgte caldina after the same happened to the last. I never had any issues with it in my caldina, which was only used in the weekends and could go several weeks without starting.

[DeeCee]

alternator appears to be working if you are seeing a high voltage at the battery when the car is running.

When you turn the car off, a battery has a residual float charge.

You need to leave the car overnight and test the voltage in the morning and let us know what that voltage is.

Sounds like the battery is just knackered.

[Adoom]

A lot of battery places like century will test your battery for free and tell you if its knackered.
Does sound like the battery

[rollaholic]

just remember toyotas are awesome!

how old is the batt? if its more than 3 or 4 years its definitely suspect

[Bling]

Voltage reading often won't show up a crap battery. If its been flat before is another killer

[Lloyd]

Unplug the distributor/coil and crank it and see what the voltage is while cranking

[BZG Wagon]

Voltage reading often won't show up a crap battery. If its been flat before is another killer

Sweet - thanks for the advice. I've told her to find a battery place and get them to test it, but from reading up from a few other places it sounds like the battery is the most likely cause.

[Leon]

Another option is a bung alternator draining the battery overnight (or some other open circuit doing same).

What happens if you unplug the battery overnight, and plug it back in come morning. If it starts, then you've got an open circuit (or even something dumb like the light in the boot) draining the battery. If it is flat in the morning, even when unplugged overnight, then you've got a dead battery.

9 times out of 10, it's a dead battery though

[1hypo3]

Another option is a bung alternator draining the battery overnight (or some other open circuit doing same).

What happens if you unplug the battery overnight, and plug it back in come morning. If it starts, then you've got an open circuit (or even something dumb like the light in the boot) draining the battery. If it is flat in the morning, even when unplugged overnight, then you've got a dead battery.

9 times out of 10, it's a dead battery though

Actually open circuit wont draw any current it needs to be a closed circuit.
You could perform a current draw test by taking off positive lead and running amp meter in series this will show if you car is using current when the car is turned off when you do connect make sure all electrical components are turned off and key is in off postion, you should have between 0.04-0.07amps with all the car dormant.
To properly test the battery it needs to be fully charged and read the specific gravity readings with a hydrometer and use a carbon pile tester to load battery if it falls below 9.5v it needs to be replaced.

[BZG Wagon]

...the plot thickens...

Tested it with a hydrometer; read 75%.
Connected it to a battery charger; medium charge.

This was shortly after a jump start, although the car wouldn't turn over when these readings were given...

This is the strangest 'flat battery' I've ever seen. It basically stopped working one day. Jumping it starts the car, but then it won't restart once the leads are off - even after a 30 minute drive. Normally I find batteries slowly give out over time, and become harder and harder to start the car with - not out the blue. But then the alternator readings look line with expectations.

I'll leave the battery on the charger for a few hours, and see if it still has its charge in the morning.
Otherwise it'll be off to the auto-sparky. Could be the starter drawing too much current?

[BZG Wagon]

Going flat overnight I take it?

Going flat in like seconds

[jondee86]

Going flat overnight I take it?

Going flat in like seconds

Had it happen with a "Good" battery. Could charge it up overnight... all
good, put it in the car and not even enough grunt to start the engine one
time. The battery was munted (been run dead flat a couple of times) but
it would take a surface charge, and look good when tested with a volt-
meter. I could drive round all day, but after sitting for half an hour, it
wouldn't start again. Car was running off the alternator.

New battery time dude

Cheers... jondee86

[rollaholic]

load tester will sort the boys from the men (or the cranking test suggested above)