Car battery - stuffed?

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2849 posts

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#2739209 5-Jul-2021 15:12

I left it on the charger till 10:30 last night and it was reading 12 v this morning.

I looked at Supercheap Auto's web site where I bought it and saw that they will test a bty for you so I carted it down to them and the guy said it had about half the new bty cranking power so I put it back into the car and it started. Went for a good 40 min run so that should have charged it up.

There must be a little constant bty drain as the radio loses its station settings.

Anyway, will make sure I run it a bit more regularly and see how we go.

Cheers, all.

timmmay

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#2739210 5-Jul-2021 15:13

Instead of running it regularly you can just charge it regularly. If it goes flat within days / small number of weeks then there's probably an electrical fault.

tripper1000

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#2739212 5-Jul-2021 15:33

+1 - Mains powered chargers can't be beat.

For the average car battery it takes 8 hours of charging to get it the last 20% of charge in. 8 hours is nothing for a mains powered charger, but it is a heck of a lot of driving and a lot of gas ($$).

It is the charging aspect of the driving that is important (the electrolyte sloshing to a lesser degree) - it's an expensive way to recharge a battery, but it is a technique frequently dispense as advice because the fact is that most people don't have a mains charger and are not competent with their negatives and positives. If you have and use a mains charger, then driving it is not necessary.

A flat car battery rapidly sulphates. A fully charge battery is unable to sulphate (but that doesn't undo existing sulpation). So for best storage life, they need to be stored fully charged, as opposed to lithium with prefers ~60% charge and NiCad which prefers cycling etc.

richms

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#2739213 5-Jul-2021 15:34

Stu:
richms:

..... I find that in Auckland traffic with the blower, lights, power steering and other stuff on it barely charges unless its at decent revs.

The blower?

I wish, but no, for the heater since its so damn cold at the moment.

Richard rich.ms

tripper1000

1619 posts

Uber Geek

#2739221 5-Jul-2021 15:56

Also, another word of warning to readers planning of driving their cars to recharge the battery, modern cars do not charge their batteries as well as old school cars.

This is because in the quest for better fuel economy & reduced emissions, the ECM shuts off the alternator for periods of time and will start it up only during periods of light engine load, such as when going down hill/engine braking (think the ICE version of re-gen braking). This can mean that driving the vehicles with a low battery is no help at all. This has proven problematic in some models (such as the Ford Ranger) where they never fully recharge their battery after mistakenly flattening it because the charging algorithm is designed for average everyday use, not recovering flat batteries.

On a related note this also can make vehicles with "smart" alternators pretty hopeless for jump-starting other flat vehicles because the donor cars alternator isn't/wont recharge the flat cars battery, so the dead cars battery impleads rather than assists in start-up (I've seen it a few times where a little old corolla succeeds in jump starting flat vehicles where a Ranger failed using the same jumper cables!)

I know that the 09 Lancer was on the cusp of this technology and shut the alternator down under wide-open-throttle conditions, and possible other times as well.

Batman

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#2739237 5-Jul-2021 16:34

question - you guys like plug in your car battery to wall charger all the time?

if you do, i presume you must disconnect the battery from the car so you don't accidentally fry the car computer?

timmmay

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#2739242 5-Jul-2021 16:51

I leave the battery connected to the car when I charge it from the mains using a car battery charger. No problems with my 2003 Corolla and I've been doing it for years, Nissan told me informally even their modern cars are ok with it, but don't take my word for it I'm just repeating what I was told.

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richms

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#2739249 5-Jul-2021 16:56

Only time I have disconnected is when using the agressive pulse mode to hopefully get more life out of a stuffed battery, since the ECUs etc all have over voltage protection which will take that pulse away. Otherwise the plug in charger is no higher in voltage than what is fine for a car to have on it. 14-15v or so.

Richard rich.ms

andrewNZ

2487 posts

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#2739281 5-Jul-2021 18:33

My boss was told his Puget alternator is only good enough to maintain the battery charge, and if the battery is flat, the car isn't capable of recharging it if jump started.

jpoc

1043 posts

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#2739336 5-Jul-2021 21:49

tripper1000:

+1 - Mains powered chargers can't be beat.

For the average car battery it takes 8 hours of charging to get it the last 20% of charge in. 8 hours is nothing for a mains powered charger, but it is a heck of a lot of driving and a lot of gas ($$).

It is the charging aspect of the driving that is important (the electrolyte sloshing to a lesser degree) - it's an expensive way to recharge a battery, but it is a technique frequently dispense as advice because the fact is that most people don't have a mains charger and are not competent with their negatives and positives. If you have and use a mains charger, then driving it is not necessary.

A flat car battery rapidly sulphates. A fully charge battery is unable to sulphate (but that doesn't undo existing sulpation). So for best storage life, they need to be stored fully charged, as opposed to lithium with prefers ~60% charge and NiCad which prefers cycling etc.

Are you sure about this? It just doesn't sound at all right to me.

Most mains battery chargers will charge at 2A so, over 8 hours you would put 16 AH into the battery. That amounts to about 20% of the total charge in a typical 80AH battery.

In a modern car, the alternator will supply between 50 and 100A.

Most of that current will be available to charge the battery and so it will take fifteen minutes to put 16AH into the battery as opposed to 8 hours with a charger.

Even a trip to the dairy will do more good than a couple of hours on a charger.

I know that you can pay the big bucks and get a faster charger but even those appear to deliver only about 15% of the current of a typical alternator.

timmmay

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#2739338 5-Jul-2021 21:52

Batteries can't always absorb the maximum current a charger can deliver, particularly when it's almost full.

jpoc

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#2739342 5-Jul-2021 22:11

andrewNZ: My boss was told his Puget alternator is only good enough to maintain the battery charge, and if the battery is flat, the car isn't capable of recharging it if jump started.

Did that car have headlights?

Did the headlights go dim if he turned on the wipers, rear screen heater and the ventilation fan?

Was there a red charge fail light shining on the dash?

If the alternator could run the lights, wipers, etc, then there would be at least 20A spare to charge the battery when the car was being used on a nice afternoon. That's as good as ten battery chargers from the warehouse.

andrewNZ

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#2739351 5-Jul-2021 23:36

We're electricians, and I agree it sounds crazy, but that was the official line from the manufacturer. Basically the alternator is undersized and only just keeps up when things are going well.

Modern cars are getting less power hungry with led lights and what-not. I wouldn't be surprised if there was a lot less than 20amps to spare. It sounded like if you only idled round on rainy nights, the battery would go flat.

And after needing a jump start, the battery wouldn't start the car again dispute the 15 minute drive home. A night on the charger had it sorted.

geoffwnz

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#2739474 6-Jul-2021 09:49

jpoc:

andrewNZ: My boss was told his Puget alternator is only good enough to maintain the battery charge, and if the battery is flat, the car isn't capable of recharging it if jump started.

Did that car have headlights?

Did the headlights go dim if he turned on the wipers, rear screen heater and the ventilation fan?

Was there a red charge fail light shining on the dash?

If the alternator could run the lights, wipers, etc, then there would be at least 20A spare to charge the battery when the car was being used on a nice afternoon. That's as good as ten battery chargers from the warehouse.

If it was a Peugeot, then:

Yes.

Most likely, yes.

No because the bulb for the dash light had failed already.

😛

MotorDrive Rallying

Groucho

524 posts

Ultimate Geek

#2739614 6-Jul-2021 11:02

mudguard: If it gets very little use you could leave it attached to a trickle charger. I've got an old school immobiliser on a Civic and it drains the battery pretty quickly.

Reading with interest. I have a 1996 Corolla with a retrofit Uniden alarm/immobiser. I can confirm the immobiliser kills the battery as have had to get the battery charged a couple of times. In summer if I leave the car for about a week I get the whirrr whirr's with a cold start and obviously a lot shorter time in winter. As I walk to work most days I'm now in the habit of going for a drive a couple of times a week when I get home. Post lockdown I bought a cheap manual charger which is rubbish with the thought I should have it as a backup but given my car lives nowhere near a power source it's a bit of a mission to use.

Has anyone had any success with those solar panels that plug into what is formerly known as the cigarette lighter to trickle charge?

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