dead battery strange observation

[ErikKiekens]

My dear fellow sailormen,
I have had to replace dead batteries a number of times over the past 30 years. Some day, they refused to start the engine; would not be charged by alternator, and even after a full night the electric charger was not able to get their voltage above 7 or 8 volts.
Now on my brand-new second-hand Dufour my starting battery won't even light the engine display, let alone attempt to start the engine. I have to use cables to connect the service batteries to do the job (without any problem). Conclusion: battery death.
HOWEVER: my multimeter reads 13 volts on this "dead" battery???!!!???
Is my diagnosis still correct?
Erik the happysailormanforvariousreasons

 

[VicS]

Id not expect 13 volts from a discharged battery Id only expect that from a well charged battery.

It does not mean of course that it can supply much current ie to a starter motor but Id expect it to light the warning lights. What happens to the volts measured directly at the battery posts when you switch on and when you attempt to start?

Suggest you get the battery professionally tested and look for bad connections etc

 

[Baddox]

I’d check the battery cables and connections for corrosion. Next, try putting the meter across the battery to measure the voltage when someone tries to start the engine. If it still reads high then you have a problem with something causing resistance in the wires.
Try measuring the voltage from +ve battery to +ve at the starter motor, more than half a volt sowing up indicates your problem is in the wire between, if not then do the same for –ve side or starter. Narrow down the search after that.

 

[ErikKiekens]

it's not the connections; because everything works well if I just connect (using starter cables) the starting battery with one of the service batteries.
I am even impressed with the ease at which the 2008 volvo penta d2-55 starts.

 

[KAL]

it's not the connections; because everything works well if I just connect (using starter cables) the starting battery with one of the service batteries.
I am even impressed with the ease at which the 2008 volvo penta d2-55 starts.

...which makes it sound even more like it's due to a problem in the connection between the battery and the starter - too much resistance somewhere along the line?

How about connecting the engine battery to the starter with your jump leads and seeing if this makes a difference?

Good luck!

 

[VicS]

it's not the connections; because everything works well if I just connect (using starter cables) the starting battery with one of the service batteries.
I am even impressed with the ease at which the 2008 volvo penta d2-55 starts.

Which suggests a bad connection between a battery post and the lead

 

[VicMallows]

Put a significant load (12v 20W bulb etc) directly across the battery terminals and see what happens (in old days I would have said just flash a wire across the battery, but too dangerous now). I have certainly seen batteries which are to all intents totally dead show an open-circuit voltage around 13v on a digital meter.

Vic

 

[fergie_mac66]

my guess is that most of the surface are of each battery plate are badly sulfated.
Each cell will have a small area unsulfated (which accepts a charge) That little bit of each plate is getting fully charged, thus 13 V

Its like its like having a brand new 5 amp hr battery !

 

[Topcat47]

Does it really work like that, Fergie? I know sulfation is a real phenomenon, but I thought if you lost plate area through sulfation, you lost potential in the cells.

 

[fergie_mac66]

Does it really work like that, Fergie? I know sulfation is a real phenomenon, but I thought if you lost plate area through sulfation, you lost potential in the cells.

not sure but it would explain ,I came to this conclusion when I had a big truck battery do that to me . I have a charger that has a desulphate cycle

Every time I connected it It went into the desulphate cycle but after 2 weeks still only showed 14% storage so I gave up and binned it

Edit though only 14% storage it showed 13.2 v !

 

[elton]

not sure but it would explain ,I came to this conclusion when I had a big truck battery do that to me . I have a charger that has a desulphate cycle

Every time I connected it It went into the desulphate cycle but after 2 weeks still only showed 14% storage so I gave up and binned it

Edit though only 14% storage it showed 13.2 v !

I've seen that happen.

 

[fergie_mac66]

I've seen that happen.

Thought about making one of these

Circuit
http://www.alton-moore.net/graphics/desulfator.pdf

Details
http://www.courtiestown.co.uk/batteries/batterydesulfators/batterydesulfators.htm

Runs off the battery Which is kept up with a trickle charger !Some how seems to good to be true! although the circuit makes sense!

 

[Plevier]

As long as you have got some charged active material left in the battery, when charged it will give (specific gravity + 0.85) volts per cell (varies with temperature).
So a typical car battery with 1.280sg fully charged will give 12.8V. (You can see 13+ freshly off charge but it will soon go.)
So yes you can have a battery badly damaged by sulphation, or paste shedding, or corrosion, and provided the acid hasn't been too much depleted by producing sulphate, you'll still get a good voltage from the bit of active material that's there, but very little capacity. The acid might still be at say 1.250 and then you'll still get 12.6V.
The OP's situation here sounds like high resistance either in his wiring - or inside the battery.
As already suggested, put a meter on the battery terminals themselves - not the cable ends - apply a load and see if the battery voltage collapses. If it does - chuck it. If not - check the wiring!