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[SR-71Blackbird]

Hi all,

Car wouldn't start today after only not being used since Thursday night.

So I took the battery out of the car and measured the voltage, 12.08

Then stuck my little 6 amp battery charger on it. After just over an hour I turned off the charger and let the charge fall to rest, it was 12.60 after only about an hour? The battery is a wet cell 100Ah 950cca so that surprised me as I don't understand how it charged so fast in such a small amount of time.


My plan is to continue charging for a few more hours and then leave it for several days in the house, not charging, and monitor its voltage.

Then if it holds its charge I suppose something in the car must be sucking out power when it is not being used.

I will report back when I have more data.


Alex

[Entwood]

A voltage that is high whilst off-load, and appears to recharge quickly, can plummet when on-load as it is indicative of a possible failing cell.

A battery may "hold a charge" (voltage) off load but be incapable of actually providing the amperage required to do anything useful, which is why batteries should always be checked using a load ..

I would stick the battery back on the car, check the voltage offload, then stick the headlights on and recheck the voltage with the lights on ...... 

[Kevin Wood]

Had the battery stopped drawing current from the charger?

Clearly, it's going to take at least 16 hours to fully charge from that charger. If it had stopped drawing current so soon, it's an indication that the battery is past its' best. Measuring the voltage isn't that reliable as an indicator of the charge level of the battery, TBH.

[AndyStobbs]

So is it starting the car again or not?
12.08 isn't DEAD flat, so it wouldn't need a full charge to float it back up.
As said you need to load it and see, couple of minutes with the high beams on will decide how good the battery is.

[SR-71Blackbird]

Thanks for the replies,

It has held a charge of 12.50 for 2 days now off the car, so I am going to charge it up overnight tonight and then put it into the car, then load test it with the head lights.

What should happen, should the voltage stay almost constant all the time the headlights are on and if if the numbers start falling then it is clear the battery is not good? How long should I leave the lights on for, 2 mins, 5 mins?

[Entwood]

Thanks for the replies,

It has held a charge of 12.50 for 2 days now off the car, so I am going to charge it up overnight tonight and then put it into the car, then load test it with the head lights.

What should happen, should the voltage stay almost constant all the time the headlights are on and if if the numbers start falling then it is clear the battery is not good? How long should I leave the lights on for, 2 mins, 5 mins?

Voltage should not drop by very much at all with the headlights on, for at least 3-4 minutes, then a slow drop may occur. IF the voltage is stable with the lights on , try getting someone to start the engine whilst watching the voltage ... it will drop but should not drop by more than 1-2 volts .. if it drops really low the battery is probably FUBAR .. it holds a voltage (pressure) but can give no current (work)

HTH

[AndyStobbs]

Voltage will fall away with the lights on. But should recover after you turn them off. Give them 2 mins and see if it will start. If it does start, turn it off and give it five minutes more.
Weather is pretty barmy at the mo so battery will give as good as it can.

You can expect to see 8v during cranking. Any lower and its best days are all behind it.