when is a battery "dead"

Submitted: Thursday, Nov 26, 2015 at 19:03
ThreadID: 130987 Views:2404 Replies:5 FollowUps:14
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HI all. I have a basic knowledge of 12 volt electrics -or so I thought. The other day I was asked to jump start a neighbours car with a "flat" battery. Lights had been left on for 4 days.
I thought it would be better to hook it up to the ctek over night rather than jump it as the owner was not intending to drive it around that much after the start. Hooked up the ctek and it didn't register on the doc meter. I then hooked up a multimeter across the terminals- it read 1.4 volts. Checked other batteries- all good. Checked the flat one again- 1.4 volts. I suggested it might be time for a new battery and left it at that. Apparently the neighbour has since jumped the car and said the battery is working fine. This has me stumped. I really thought 1.4 would mean non redeemable. Any thoughts? Ta doc.
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Reply By: Roachie Silverado - Thursday, Nov 26, 2015 at 19:15

Thursday, Nov 26, 2015 at 19:15
It depends on a number of factors....not the least of which is "how old is the battery?"

For example, if you took a brand new battery and drained it down to that low level, then it is entirely possible that it could be brought back up and live to start another day.

However, the older the battery is (and hence at some advanced stage of it's life cycle), then the less chance there would be of resurrecting it.

There is no black and white answer to that question (IMHO).

Roachie
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Follow Up By: oz doc - Thursday, Nov 26, 2015 at 19:37

Thursday, Nov 26, 2015 at 19:37
Ok. didn't check the age of the battery. My other concern was a comment my father made that jump starting a battery so severely discharged could damage the starting vehicles alternator. ? true do you think. doc.
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Follow Up By: Bonz (Vic) - Saturday, Nov 28, 2015 at 17:58

Saturday, Nov 28, 2015 at 17:58
I cant see how it would affect the starting vehicles alternator...
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Reply By: Bushranger1 - Thursday, Nov 26, 2015 at 19:49

Thursday, Nov 26, 2015 at 19:49
My wife has a bad habit of leaving the headlights on our Hilux (no warning buzzer).
Usually not noticed for a few days at a time so the battery is well & truly discharged.

If its dead flat my multi stage "smart charger" will report an error & not start the charge cycle. In this case I leave the battery on my older style basic charger for an hour or so to get a bit of life into it then swap to the multi stage charger to give it a full charge cycle.

If it gets flattened when she goes to work I just go down & jump start it then when she gets home it gets connected straight to the multi stage charger.

Either way the battery is still going strong.

Cheers
Stu
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Follow Up By: Gronk - Thursday, Nov 26, 2015 at 20:00

Thursday, Nov 26, 2015 at 20:00
The battery is still going.......debatable on how many times you can abuse a battery like that before it goes to heaven, but as long as the price of a new one doesn't bother you too much, or the fact that one of the times you go to start the 4wd it is really cactus and won't recover..

Maybe your wife needs another bad habit, just not that one ...LOL
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Follow Up By: Bushranger1 - Thursday, Nov 26, 2015 at 20:30

Thursday, Nov 26, 2015 at 20:30
Yes we do have words about it every time it happens!
I usually make the comment that a pilot doesn't forget to put the wheels down when landing a plane & that tends to go down like a "lead balloon".

Oh that's right there IS a warning for that.
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Follow Up By: Member - Trevor_H - Thursday, Nov 26, 2015 at 22:49

Thursday, Nov 26, 2015 at 22:49
On my old Hilux(s) I wired another horn type relay into the headlight circuit on the switch (earth) side and triggered this from the diesel control cut off solenoid. Shut down the engine and break the headlight relay earth....headlights off. I figured a warning was pointless when you could just turn off the headlights. Found the headlight relay got power direct from the +ve side of the relay and was earthed by the headlight switch. It was in this earth wiring I inserted the additional relay. For a petrol motor, the ignition coil +ve could have been used.
Saved me several times.
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Follow Up By: Member - John - Friday, Nov 27, 2015 at 00:42

Friday, Nov 27, 2015 at 00:42
Fit a headlight on alarm or new wife............................... LOL, is it Friday yet?
John and Jan

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Follow Up By: Bushranger1 - Friday, Nov 27, 2015 at 07:14

Friday, Nov 27, 2015 at 07:14
Thanks for the info about wiring up the headlight warning alarm.
Planning on updating soon to a newer model so won't need to spend time doing that on the old girl :-)
Talking about the car that is!

Certainly don't need to update the wife as she's perfect in every other way. She loves going out bush at every opportunity so what more could I want.

Cheers
Stu
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Follow Up By: Gronk - Sunday, Nov 29, 2015 at 16:48

Sunday, Nov 29, 2015 at 16:48
Headlight warning alarm.....that used to be a bit of 4 x 2 didn't it ??? LOL

Probably not allowed to do that any more ??? LOL

Perfect in every other way ?? C'mon, never seen one THAT good !! LOL
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Reply By: Sand Man (SA) - Thursday, Nov 26, 2015 at 20:39

Thursday, Nov 26, 2015 at 20:39
Hi Oz Doc,

1.4v doesn't sound right to me.
10.4v is dead flat. Perhaps this was the reading you thought you saw?
Each cell in a lead acid battery should supply about 2.14v in good nick.
A 12v battery is made up of 6 cells giving a total of 12.8v fully charged.

If you were reading 1.4 volts, it was more than likely a bad connection of the meter probe on one of the terminals. That is the only explanation I can think of as to why the battery would recover from a "jump start" (ie being subsequently charged by the vehicle alternator). Perhaps the terminals had been moved and a better resistance connection subsequently provided.
A high resistance connection of the original cable connections would be the most likely cause if the battery is now working OK.
The Ctek would just see a poor battery condition and would not initiate a charging current. The built in logic would register a fault condition.
The multimeter across the terminals would also be though the high resistance connection a give an erroneous reading, unless you placed the probes on the lead centre poles themselves, in which case ignore all the logic I have stated above:-)

Bill


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Follow Up By: oz doc - Thursday, Nov 26, 2015 at 22:57

Thursday, Nov 26, 2015 at 22:57
1.4 didnt sound right to me either. Had my glasses on though. Checked another battery with the meter -all good. Measured right across the posts themselves not the clamps. Got me stuffed. Unless the battery is not as "good" as we are led to believe. Time will tell. Doc
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Follow Up By: Bushranger1 - Friday, Nov 27, 2015 at 07:23

Friday, Nov 27, 2015 at 07:23
Hey Oz doc,
I get the battery place in town to do a quick load test every year just to make sure it's all ok & won't let me down when I need it most.
They give you a computer printout on the spot of the performance of the battery. It's free of charge & I make the decision then & there as to whether I will replace it or use the battery for a bit longer depending on where I am taking the vehicle in the next 12 months.

Cheers
Stu
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Reply By: TomH - Thursday, Nov 26, 2015 at 22:57

Thursday, Nov 26, 2015 at 22:57
Had one do that on my sons car when brake light switch went bad. Got 1 .6 V on my meter. Confirmed by Battery World Presumed it was stuffed but Battery World slow charged it for 3 days. Put it back in the car and its still going Ok after at least 15 months.
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Reply By: Member - Phil G (SA) - Thursday, Nov 26, 2015 at 23:34

Thursday, Nov 26, 2015 at 23:34
The Ctek did nothing because it thought there was a fault because the battery voltage was 1.4V.
What I would do is simply hook the battery up to my 25A regulated power supply I have in the shed.
After the battery has got some charge and voltage back, then hook it up to the CTek.

Alternatively, if you want to jump start it, I would run the donor vehicle at fast idle for a while so the battery gets some charge back. Then turn switch off the donor vehicle and attempt to start the one with the flat battery.
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Follow Up By: TomH - Friday, Nov 27, 2015 at 07:51

Friday, Nov 27, 2015 at 07:51
I find it better to hook them up like you say for 15 mins and then while still connected start the flat one, then disconnect the donor Then let it run for a while to boost its battery .
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Follow Up By: Nomadic Navara - Friday, Nov 27, 2015 at 08:53

Friday, Nov 27, 2015 at 08:53
Quote "The Ctek did nothing because it thought there was a fault because the battery voltage was 1.4V.
What I would do is simply hook the battery up to my 25A regulated power supply I have in the shed.
After the battery has got some charge and voltage back, then hook it up to the CTek. "

The reason the CTek did not start charging is that they need to see a certain voltage from the battery to determine there is a battery there. This is a feature of many of these types of charger. Some of them are multi battery voltage models, these ones need that battery input to determine whether to set up as a 12 or 24 V battery charger. Getting some charge into the battery like you did is the recommended way of getting those chargers to start.

I suggest all you who have these styles of chargers search through your operating instructions to discover the minimum voltage from your batteries is necessary to allow your charger to start charging.


PeterD
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Follow Up By: Member - Phil G (SA) - Friday, Nov 27, 2015 at 09:44

Friday, Nov 27, 2015 at 09:44
Gday Tom,
The reason why I have the donor vehicle turn off during the start is to protect it's alternator. Seen it happen where the good smaritan attempts to jump start another vehicle and finds their alternator is no longer. Probably more likely if the flat vehicle won't start and there are continued attempts at cranking it.

Gday Peter,
Glad you agree. I haven't had the opportunity to try it, but wonder whether the supply mode on some chargers would bring the voltage up enough to get the charger to work.
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Follow Up By: Nomadic Navara - Friday, Nov 27, 2015 at 10:48

Friday, Nov 27, 2015 at 10:48
Quote "Glad you agree. I haven't had the opportunity to try it, but wonder whether the supply mode on some chargers would bring the voltage up enough to get the charger to work."

If your battery charge is capable of starting in PSU mode without the battery attached then I see no reason that it can not be used as a PSU to do the commencement phase of recovering your battery.


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