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Battery total discharge

4K views 23 replies 7 participants last post by  scannyman 
#1 ·
Hi guys a very strange thing happened earlier. I drove about 40 miles and turned off the engine at my destination. After about 30 mins I went to start the engine to return home and the battery was absolutely dead, not enough in it to even turn the engine. The ignition lights were normal and there wasn't any signs of a problem during the drive down. I had the AC and side lights on as well as the radio whilst driving.
Would I be right in assuming this is an alternator charging issue or is it something more serious ?
Any suggestions are much appreciated.

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#3 ·
Hi leafy thanks for your reply.
I managed to get a jump start and it drove back without any problems. I put a multimeter on it and with every electrical item switched on it was reading 14.07 volts with the engine running. I have read that if it's under 14.2 there may be an issue with the alternator. I'll check the cells in the morning and report back. I do have a battery/ alternator tester as well somewhere, I'll hunt it down and see what that says.

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#6 ·
scannyman said:
Hi Ahto does that mean even though the multimeter reads 14.07v it is really only charging at 12.5v ?

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Yeah, with a multimeter. I was scared at first that maybe my alternator was bad. I was like from the start it charged like 15 minutes with 14.2v then the current sensor sees that the amps going to the battery are reduced, then it stops charging. Have not experianced with other makes with charging current sensor on the neg battery lead.
I did not know back then, how the system works. in colder climates, newer QQ and x-trail had battery problems, but they clamied it was batteryis from the factory.

http://www.nissantechnicianinfo.mobi/ht ... ntrol.html

In the Electronic Service Manual (ESM), section CHG-Charging System, vehicles with variable voltage control systems, which use the IPDM E/R to provided the PWM signal to the alternator, as described in this article will have a section titled POWER GENERATION VOLTAGE VARIABLE CONTROL SYSTEM and a System Diagram similar to the one above.

A Variable Voltage Control system is different in that it monitors all power usage via the battery current sensor/ This allows the ECM to control the alternator in two major ways:
It keeps the load as low as possible to maximize fuel economy.
It makes sure the alternator supplies enough power for all of the systems that are operating.
 
#7 ·
Just carried out some tests
With engine off battery test is 12.6 v, with engine on it is 14.16 v. Under load it is 14.16-14.20.
The battery/alternator tester shows only 2 lights for the battery and no lights for the alternator with the engine on, as in the picture.
With no lights showing for the alternator this suggests a faulty one but according to the multimeter it seems to be charging ok but only just reaching the recommended charge which I believe is 14.2v.
I'm confused with conflicting readings .


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#12 ·
What is the voltage on the leads and on the battery posts? How old is the battery?

If the battery is good, then at full load the alternator should outbut at least 13.5v at the leads. And when you measure the voltage on the battery posts and the reading is way off, like 12.7v then there is bad connection.
Acceptable votage drop is 0.1-0.2 v between leads and posts.
 
#14 ·
From what's been said, I would suspect the battery. If the alternator is providing 14.2v on absolutely full load, there probably isn't much wrong with it. Older batteries could be prone to sudden discharge.

You don't say how old your T31 or battery is, but battery management systems haven't generally been fitted unless the car has stop/start or regen braking assistance. Some kind of control is needed in order to provide headroom for charge dumping when braking etc. If fitted with a battery management system (BMS) it is usually fitted to the negative terminal and controls battery charge level to around 80%. Easily identified. Mine's an early T31 and no battery management system.

The real test is how the battery changes with load without engine running and how voltage changes overnight. I recently had battery problems on our Skoda. The first symptom being that the Stop/Start system didn't appear to be working, then I got a low battery warning. Put it down to reduced use during Covid restrictions. Charged the battery off the car using an "intelligent" charger with maintenance mode (charge level varies with battery state/condition, switches to trickle when charged). When re-fitted, the voltage was 12.8v. Alternator took it to 13.3 v then reduced to 12.6v. It dropped to 12.2v overnight then to 11.9v. After checking for current drain, replaced the battery. Original was an EFB type, replaced with current recommentation - AGM. With BMS active, the new battery barely drops below 11.9v on starting, boosts to 14v or so for 3-4 minutes then settles to 12.6v until braking when it jumps briefly to 14.7v. Figures are for AGM, EFB and standard wet would be slightly different.
 
#15 ·
Ahto42 said:
What is the voltage on the leads and on the battery posts? How old is the battery?

If the battery is good, then at full load the alternator should outbut at least 13.5v at the leads. And when you measure the voltage on the battery posts and the reading is way off, like 12.7v then there is bad connection.
Acceptable votage drop is 0.1-0.2 v between leads and posts.
Hi Ahto , not sure if I need to remove the leads from the battery to test the voltage at them but I didn't anyway as I don't want to further complicate matters as I believe people have had problems after re-connecting them although obviously they do have to come off should the battery need replacing. The battery itself reads 12.35 after standing overnight. With the engine on it reads 14.16 on idle and 14.20+ with a constant 1500 revs and under full load. I believe this is a healthy charge from the alternator.
There was a slight hesitation at start-up so it seems that the battery is losing too much charge overnight .
What happened the other day when it lost all charge after standing for 30 minutes I have no idea. The other mystery is why the battery warning light is still as bright as ever even when it was drained.
I've had the car 5 years without changing the battery and the car is 9 years old so I'm guessing it's still the original battery. It only does short 10-20 min journeys these days with the odd long one ...like the other day...so obviously that doesn't help. Any further thoughts ?

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#17 ·
HI AMB, think I agree with you . It's pointing towards a faulty battery now. I think it's the original so 9 years out of it is very good I think. It was quite alarming that after a 40 min drive and standing for 30 mins it lost all power to even turn over the engine. Once it'd been jump started it was fine again and drove back home without any signs of a problem...this in itself suggests the alternator is fine does it not ?

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#18 ·
Colster said:
I would say that your battery has been replaced previously, probably with a used one. From your picture, your battery has removable cell tops. Nissan OE are usually "maintenance free". Your testing does suggest a faulty battery.
Ah ok. I didn't realize that. The previous owner did 40k in 4 years from new which is average mileage but maybe doing a lot of stop start.
Thanks colster.

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#19 ·
Just took it in and had a proper battery test done. It was operating at 59% so was obviously shot. When it was removed one of the cells was very low but this wasn't evident while it was on the car. Needless to say I had a new battery. Hopefully problem solved [emoji849]

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#20 ·
scannyman said:
Just took it in and had a proper battery test done. It was operating at 59% so was obviously shot. When it was removed one of the cells was very low but this wasn't evident while it was on the car. Needless to say I had a new battery. Hopefully problem solved [emoji849]

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Yes, hopefully problem solved. As Colster said, looks like a non-original older style battery. They do tend to degrade as the plates sulphate up and also grow "whiskers" on the plates which can short out a cell. I bought a cheap Ebay (£6) combined battery voltage monitor, dual USB charger that plugs into the power socket and provides an extension socket. Gave a lot of peace of mind until I was satisfied that it had been the battery.
 
#21 ·
Good idea AMB,, something else to add to my list. I have a OBD plugin reader , I'll see if that gives me a reading of the charge .
Checked the new battery this morning and it read 12.63 v on the multimeter so happy days.
One thing that puzzles me is the old battery had a cell that was a good 2" lower in fluid than the others but it looked exactly the same as the others when it was in situ. It was only evident after it was taken out of the car.

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#23 ·
My guess from what I am reading is that a previous owner removed a good battery when they sold the car and replaced it with a duff old one, just in order to sell it but keep the decent battery. Any car battery that drops to 12v or below is effectively flat. It doesn't sound like there is any problem with the charging system, so hopefully replacing the battery will have solved the problem.
 
#24 ·
I did well to get 5 years out of the old battery. The new one has been on 1 week and everything is ok now. I bought a volt meter that plugs into the power socket which gives me constant readings of the voltage. 3 year warranty on the new battery which I thought was quite good.

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