Drained battery
ed1max - 20/1/13 at 08:45 PM
The battery on my Westie goes flat after a few day in the garage with the ignition and isolator keys removed.
The battery is fairly new,any ideas?
Thanks and regards
Eddie
Daddylonglegs - 20/1/13 at 09:30 PM
If you've got an ammeter that will handle a few amps, put it in the live feed from the battery and monitor it. If there is any significant
current drain, try removing each fuse in turn and see if it stops drawing. if you find one that does, at least you know which circuit it is. HTH
gremlin1234 - 20/1/13 at 09:50 PM
does it have a (fused) bypass on the isolator?
else its a failing battery, and should be replaced under its guarantee
chrism - 21/1/13 at 12:47 AM
Are you fully charging it up after it is drained and not just jump starting it, as Ive read recently in a few places that an alternator wont fully
charge a drained battery it will only top a battery up. Apparently the old dynamos would fully charge a flat battery.
So if a battery is drained flat it would require using a charger to fully charge it back up again.
jabs - 21/1/13 at 07:56 AM
quote:
Originally posted by chrism
an alternator wont fully charge a drained battery it will only top a battery up. Apparently the old dynamos would fully charge a flat battery.
That's because an alternator needs some voltage to excite it to create the magnetic field whereas a dynamo has magnets and just generates power
when rotated
Slimy38 - 21/1/13 at 08:08 AM
quote:
Originally posted by chrism
Are you fully charging it up after it is drained and not just jump starting it, as Ive read recently in a few places that an alternator wont fully
charge a drained battery it will only top a battery up.
A fact a lot of people are finding out in the winter months when it gets harder and harder to start their cars...
britishtrident - 21/1/13 at 08:17 AM
There are a number of things it could be but the first thing to do is put the battery on a slow( low current rate )charge for 12 to 30 hours.
Once taken off charge rest the battery for a couple of hours and then check the voltage across the battery terminals in the current UK sub zero
weather expect on a fully charged battery to see about 12.65 to 12.75 volts in more normal UK weather expect to see 12.8 to 12.9 volts --- any
more indicates an over charge.
Once the battery is fully charged you can do some tests.
(1) Cranking volts drop test --- measure the voltage while cranking the engine, if the voltage rapidly drops below 10v suspect a dead cell in
the battery.
(2) Charging voltage -- measure while you the run the engine at about 1500 to 2,500 rpm, with the head lights switched on the voltage
should read 13.4 to 14.9 volts. Then watch the voltage while you switch the lights of, the the voltage should not jmp above 14.9 volts.
(3) Current leak back test ---with the ignition and everything else off disconnect the battery and connect an ammeter between battery cable and
the battery. If the ammeter shows more than a few milliamps you have a current leakage that needs to be tracked down. The prime suspect for
current leakage are alternators, radios/cd players and alarm systems. Alternatively just disconnect the battery for a week, if when you
reconnect the battery the car starts as normal then you have a current leak back problem.
To check for current leakage through the alternator simply disconnect ithe alternator if the current drops significantly the alternator diodes
are goosed.
Remember to reconnect the alternator before starting the engine.
If after these tests you suspect there is current leaking through some other part of the electrics you need to measure the current through each
fuse in the system, ideally you want one of these they are available for both blade and mini-blade fuse fittings. Automotive
Current Tester - Mini ATM APM Blade Fuse Box Board Meter Circuit Test 
[Edited on 21/1/13 by britishtrident]
ed1max - 21/1/13 at 12:32 PM
Thanks to all for the advice it is appreciated.
ed1max - 21/1/13 at 12:37 PM
Thanks to all for the advice it is appreciated.