Subject: [Mgb-v8] Battery drain

From: Barrie Robinson <[email-masked]>
Date: Wed, 17 Jul 2019 15:45:51 -0400

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Hello folks,

After leaving my MGB GT V8 for a few days - maybe 4 or 5  I find the 
battery is completely flat.  Did that 3 times.  So I took the battery 
out, charged it and waited 3 days.  The voltage dropped from 13.15V on 
Sunday 3pm to 12.91V 3pm Wednesday which does not seem to indicate that 
it is the battery's problem?    I did have a radio fitted but cannot say 
if it was after that that the battery went flat.   So any tips on how to 
find out what is going on would be appreciated (and thank you in 
advance) - I will try to disconnect the radio but that is a pain - I 
have to find the special tool to slip it out !!!!   But surely if the 
radio is off (blank screen) it should be /off./ By the way my new $$$$$ 
radio with windscreen mounted antenna cannot bring in 91.5FM or 99.1FM, 
the only stations I listen to because they do not have adverts.......but 
my cheap $ new portable one can get them inside my car !!!!!

Cheers
Barrie

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    <font size="-1"><font face="Arial">Hello folks,<br>
        <br>
        After leaving my MGB GT V8 for a few days - maybe 4 or 5  I find
        the battery is completely flat.  Did that 3 times.  So I took
        the battery out, charged it and waited 3 days.  The voltage
        dropped from 13.15V on Sunday 3pm to 12.91V 3pm Wednesday which
        does not seem to indicate that it is the battery's problem?    I
        did have a radio fitted but cannot say if it was after that that
        the battery went flat.   So any tips on how to find out what is
        going on would be appreciated (and thank you in advance) - I
        will try to disconnect the radio but that is a pain - I have to
        find the special tool to slip it out !!!!   But surely if the
        radio is off (blank screen) it should be <i>off.</i> By the way
        my new $$$$$ radio with windscreen mounted antenna cannot bring
        in 91.5FM or 99.1FM, the only stations I listen to because they
        do not have adverts.......but my cheap $ new portable one can
        get them inside my car !!!!!<br>
        <br>
        Cheers<br>
        Barrie<br>
      </font></font>
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Archive: http://www.team.net/archive

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From: "PaulHunt73" <[email-masked]>
Date: Thu, 18 Jul 2019 09:47:10 +0100 M1IwWA3AW9UwP7Y3XR6IdpBOC+Dm9+iU3IifGwX8GIIWZ+G4FrMNXlIy

That's a significant drain, even with alarm, radio and clock it should last
for 2-3 weeks.

Your battery voltage off-car seems OK, but that is not a good indication of
the amount of charge i.e. cranking power.  If you put it back on the car
after three days and it cranked OK that does indicate the battery itself is
OK - up to a point.

However the Lucas Fault Diagnosis Manual states that if a battery becomes
25% discharged then the on-board charging systems will never get it back to
full capacity, and if it has become completely discharged they will never
put back more than 50% capacity.  For that reason a flattened battery has to
be boost charged for a period to restore full capacity.  Using a
conventional charger this means charging at 16-17v for a couple of hours in
a well ventilated space.  Or you can use one of the more sophisticated
'maintenance' chargers but only if they have a 'recovery' program, and not
all do.  These charge using pulses of up to 20v.

But back to the drain.  If you have an analogue meter switch to its 12v i.e.
VOLTS range and connect it in place of the battery earth lead.  With no
drains on a car with an alternator you should see a few volts registered.
If it shows 12v there is a drain.  In that case the first thing to do is
unplug the alternator, and if the drain drops to zero that is the culprit.
With the few volts registered unplugging the alternator should also drop it
to zero.  But if still at 12v start disconnecting things like your radio,
the purple circuit fuse, remove browns from things like the ignition switch,
lighting switch, starter relay, hazard fuse and so on, looking at the meter
each time.  If still there remove the browns from the starter solenoid, and
finally the battery cable from the solenoid, but normally it will have been
discovered by now.

You can also do this with a digital meter but they are far more sensitive
and will show 12v even with just the normal alternator leakage, and may not
fully drop to zero with that disconnected if there is dampness anywhere.

PaulH.
----- Original Message ----- 

After leaving my MGB GT V8 for a few days - maybe 4 or 5  I find the battery
is completely flat.  Did that 3 times.  So I took the battery out, charged
it and waited 3 days.  The voltage dropped from 13.15V on Sunday 3pm to
12.91V 3pm Wednesday which does not seem to indicate that it is the
battery's problem?

[email-masked]