Classic cars forum & vehicle restoration.

L5Foye · Posted: Sun Jul 08, 2018 9:59 am Post subject: Battery Drain

After a long term restoration, I put a new battery in my Austin 10 Cambridge (12 volt) . Within a day and a half, the battery went from 12.8 volts to less than 1 volt. Nothing was switched on. What could cause the battery to drain so quickly? I haven't yet attempted to start the car but everything was working fine before restortaion started..

ukdave2002 · Joined: 23 Nov 2007 Posts: 4104 Location: South Cheshire

1v is incredibly low for a 12v battery, have you measured the SG in the cells? Or is it a sealed battery? I wouldn't rule out a faulty battery.

Disconnect the battery, and with everything switched off measure the resistance between the battery connectors, for all practical purposes it should be infinite.

Dave

L5Foye · Posted: Sun Jul 08, 2018 11:16 pm Post subject:

Thanks Dave for your reply.
I have had the battery tested and it is ok. Would a faulty regulator or the wrong polarity of the dynamo flatten a battery?

Peter_L · Posted: Mon Jul 09, 2018 3:15 am Post subject:

If you have or can acquire a multimeter with Amps (Ampere) measurement, put it in series between the end of the earth lead and the earth post of the battery. With ignition and all switches off there should be no current flow.

If it is not digital, check polarity by using interior light to give a small load.

I suggest using the earth side of the battery because you don't have to worry about connectors touching the bodywork and causing a short.

Some multimeters have a current selector switch, so start with it at Max and switch it down. You should get a zero reading even at the most sensitive, unless you have a car clock.

jp928 · Joined: 07 Jun 2016 Posts: 249 Location: Australia

Sounds like failed dynamo cut out, but if it was trying to motor the dynamo it should have been audible, or let some smoke escape. Not many chargers will recover a 12V lead acid from 1V? My very old simple charger wont look at a battery that low.
jp 26 Rover 9

alastairq · Joined: 14 Oct 2016 Posts: 1950 Location: East Yorkshire

Quality control these days is left to the customer.
Far easier & cheaper to dole out a new battery in exchange.....keep going until one gets given a good 'un?

Or, so it would appear, from a neighbour's recent experience? According to the local garage, swapping new dud batteries is becoming much more common.