Jump Starting flat 6V battery

panhead_pete

panhead_pete

Senior Member
Hi from Japan


My coupe finally arrived here today and with no surprise the battery is very flat. I have a 6v/12v charger but its one of the newer types that seem to need a reasonable residual charge in the battery before it works and this battery is too low for the charger to work.



Can I jump start the car with a 12V battery without causing any harm?



Thanks
Pete
 
It would be better to just jump the battery without starting the car. Maybe 10 seconds or less. Then put the charger on it and give it a good deep charge. Pay attention to polarity!
 
I have jump started 6 volt batteries with 12 volts many many times over the years never a problem . There is a recent thread on this ,look it up .

John in Suffolk County England . weather was cancelled today .
 
As a teenager unable to afford a new 6V battery, I jump started my Model A many times with a 12V battery.
 
The model A generator may have a problem if you get it started. The battery voltage is what regulates the system. If voltage is very low then it will be taxed and could do damage. If you have an alternator conversion then it will just put out a real heavy charge trying to charge a low or sulfated battery up and can put a heavy strain on the fan belt and water pump as well as the alternator.

I would recommend finding a good 6-volt battery charger or replace a bad battery before it costs you more for something else.
 
Ah sorry thought I had posted on this yesterday.



Its confession time and I feel a bit like a muppet. After leaving it somewhat frustrated and going home for lunch it occured to me in my haste to get this sorted I over looked there was an alternator fitted to the car and sure enough when I checked after lunch it has a 12V battery..... apologies for the wasting your time with this thread although I did learn a lot from it that I may have to use in the future.
 
Especially if the battery is completely dead, you should trickle charge for 24 hours. Killing a battery down to nothing is VERY hard on it and just a quick jump and driving around a bit may bring it back to where it'll start again but if you want to try to salvage as much health out of the battery as possible, you can't beat a trickle charger on for a long period. Also, some alternators will have a parasitic draw on the battery, best to use either a battery maintainer or a battery disconnect. In the long run, a good quality battery maintainer will pay for itself MANY times over.
 
At least this should solve the OPs battery charger problem. Charge it up or have it tested if there are charging problems. The alternator will still have a problem with a bad battery, A battery that sets more than a month can be sulfated more than a person might think and may not come back from the dead.
 
Yeah as general rule a battery that goes completely flat below 11 volts particularly for an extended time period like this, should be thoroughly charged and then tested for defects such as a shorted cell. They don't like that at all. It won't necessarily ruin a battery but it is possible. A defective battery can damage the alternator, which in turn can also damage a new battery. A hard sulfated battery is particularly difficult to recharge, I've had good luck with lightly sulfated batteries by "cycling", discharge the battery down to about 50% and trickle recharge at a low amp rate for a day or two. Sometimes this takes a couple cycles. This is where "dumb" chargers are useful.

For all that, if the battery in question is more than a few years old it's probably trashed by now without a lot of contortions like I described. Battery Tenders and float chargers are our friends.
 
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Im going 12 volt on my 440ic, changed the starter to 12 volt already, Im needing to know what size 12 volt battery do I need to use, the battery base size on the dozer is 9 by 8 I know it was built for a 6 volt battery so hopefully I can get a battery to fit the base. Any ideas?

Thanks Don
 
Used the old standby many times. Get out of the car and push. Pop the clutch..........good to go!

Check the alternator, it may a 6 volt unit. Don't assume all alternators are 12 volt.
 
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