Diagnosing potential battery/alternator problems

[GreenGoddess]

I think the battery or alternator on my car may be faulty. The radio/cassette in my car has been doing strange things for the last few months and a couple of weeks ago my indicators (turn signals) stopped working until I got home and charged the battery.

When my car is parked in my garage I always have a C-TEK battery charger/conditioner plugged in. Therefore the battery is always fully charged when I first take it out for a drive. Today I noticed that the voltmeter on the dash was showing 11 volts (almost in the red) when motoring along at 60mph. I assume it should be at least 13 volts.

After each time I've driven the car, I bring it home and plug the C-TEK charger in. When I do, the charger always shows that the battery is low. After charging the battery, I put my own voltmeter across the battery terminals with the car switch off and unplugged and was surprised to get a reading of 16 volts! 

I am therefore thinking that the alternator is not charging the battery as it should. Does that sound like a plausible theory? As you can probably tell, I am not exactly an expert at car maintenance.

[andydclements]

I can't recall on the TE, but on the SE the alternator needs the battery warning light to be functional else it will not charge, so first check, does the battery light come on when you simply turn the ignition key to on/ run (not engaging the starter)?

Next simple check is whether the drive belt is overly slack. beyond that, I'd suggest you need to check with volt meter and properly diagnose rather than start assuming particular causes of the apparent fault..

[Rambo]

Your battery is totally f----ed. Of your alternator is totally f----ed 🤔 Very easy to check out either or both. 

[TAR]

A fully charged car battery should read 12.6v or above, if it's fully charged.

12.5v indicates its OK but may need a charge soon. 12.1v - 12.4v indicates that it needs charging. Less that 12.1v means the battery is flat.

Check this with the battery connected or disconnected without the engine running.

To check the alternator, start the car and check the voltage across the battery. If the battery was fully charged, you'll see around 13v which is a floating charge. If it's higher and up to 14.7V, the alternator is providing a charge to the battery. Lower than 12.5v or above 14.7v would indicate a bad alternator (assuming you battery tested OK in the previous test).

Also check this... 

3 hours ago, andydclements said:

I can't recall on the TE, but on the SE the alternator needs the battery warning light to be functional else it will not charge, so first check, does the battery light come on when you simply turn the ignition key to on

   

 

[paulbrown22]

If the battery is really at 16V after being on a CTEK it's presumably fairly knackered then. Unless you accidentally have your CTEK on it's recondition mode which from memory puts out about 15.8V, and you tested as that part of the charge programme finished?

If you have a volt meter and/or clamp meter you can do some load testing of the battery and check the alternator output when running. It's quite possible the alternator is also screwed - the alternator rectifier on one of my boats went wrong a few years back such that the alternator was putting out close to 18V and frying the battery...

[Rambo]

11 hours ago, TAR said:

A fully charged car battery should read 12.6v or above, if it's fully charged.

12.5v indicates its OK but may need a charge soon. 12.1v - 12.4v indicates that it needs charging. Less that 12.1v means the battery is flat.

Check this with the battery connected or disconnected without the engine running.

To check the alternator, start the car and check the voltage across the battery. If the battery was fully charged, you'll see around 13v which is a floating charge. If it's higher and up to 14.7V, the alternator is providing a charge to the battery. Lower than 12.5v or above 14.7v would indicate a bad alternator (assuming you battery tested OK in the previous test).

Also check this... 

   

 

Good advice 👍

[Bibs]

If you've no idea how old the battery is, for the sake of £60-70 I'd replace it so you've a known good start point with it. They don't last forever, even on a CTek or similar.

[Rambo]

Good idea. That's what I did with my Evora

No affiliation, but try TAYNA batteries. Excellent, next day service, competitively priced and very good to deal with if there are any problems.

Customer focussed, and you can't say that about many companies these days.

https://www.tayna.co.uk/car-batteries/?gclid=Cj0KCQiAtbqdBhDvARIsAGYnXBOWzSkrKWs2WLQ9DXtmOpcbttnHrQF4scUQz4HK1p2r6L8hA5p4AD0aAmd2EALw_wcB

[ramjet]

14 hours ago, paulbrown22 said:

.......one of my boats.......

One? Showoff.  

[GreenGoddess]

Thank you all so much guys. After reading all your advice I plan to do the following:

• I'll set the C-TEK to re-condition the battery today.
• At the weekend I will disconnect the charger and measure the voltage across the terminals of the battery. If it is lower than, say, 12.3v I will replace the battery.
• If the battery is OK, I will check the tension of the alternator drive belt. If it's loose I will try to tighten it.
• I will run the engine and measure the voltage across the battery terminals. If it's outside the range of 12.5-14.7v then I will look at getting the alternator repaired or replaced.

Either way, I will report back with my findings.

[paulbrown22]

1 hour ago, ramjet said:

One? Showoff.  

To be fair, I only have one Lotus, unlike most!

[paulbrown22]

It's worth doing some basic load testing of the battery too after charging, i.e. turn on your headlights for a few minutes and see whether the voltage holds. It might hold steady after a charge with no load, but as soon as any load is applied, it plummets.

[GreenGoddess]

OK, the battery has now been plugged into the C-TEK for 24 hours on "recondition" mode and is showing as fully charged.

I just disconnected it from the charger and then turned on the main beams for 2 minutes to "get rid of any residual current" (as per some advice I saw on a YouTube video).

I then measured the voltage across the battery terminals. It was 16.5v and rising.

I then removed the battery from the car completely and let it stand for 10 minutes. I measured the voltage again and it was almost 18v.

So, I think I can now assume that the battery needs replacing. I've never heard of a battery giving out excess voltage before. That may be the reason why my car radio has started going nuts and my indicators have been doing silly things.

My next question is... can I check the alternator to see if it is outputting the correct voltage before I replace the battery? Or do I need to get a new battery first?

[Rambo]

From the web....

"18 volts is gross overcharging and almost certainly a bad alternator. That much of an overcharge will destroy a battery rapidly and if nothing else in the electrical system has been damaged you are very fortunate"

[GreenGoddess]

Eek! I’ll get a new battery but is there any way I can test the alternator output before I change the battery? 

[paulbrown22]

That battery sounds like it's completely fried, so I'd swap it out anyway. And then once the new one is fitted, have your volt meter on it when you first start the car and monitor closely, and/or get someone else to start the car for you so you can stay at the engine bay. If it does instantly start to go above 14.5V then just switch off the engine and get the alternator fixed/replaced, but I don't think a few seconds over voltage is going to trouble a new battery too much - your Ctek on recondition pushes it up to 14.8 I think anyway to desulphate the plates.

[GreenGoddess]

3 minutes ago, paulbrown22 said:

That battery sounds like it's completely fried, so I'd swap it out anyway. And then once the new one is fitted, have your volt meter on it when you first start the car and monitor closely, and/or get someone else to start the car for you so you can stay at the engine bay. If it does instantly start to go above 14.5V then just switch off the engine and get the alternator fixed/replaced, but I don't think a few seconds over voltage is going to trouble a new battery too much - your Ctek on recondition pushes it up to 14.8 I think anyway to desulphate the plates.

Thanks Paul. Do you know if the alternator on these cars has a separate regulator than can be changed? Or do I need to buy the complete alternator unit?

[drdoom]

I'd also have a read with voltmeter when the C-TEK is connected. Is it a valid strategy applying a "conditioning" exercise to conventional lead-acid batteries? 

[GreenGoddess]

24 minutes ago, drdoom said:

I'd also have a read with voltmeter when the C-TEK is connected. Is it a valid strategy applying a "conditioning" exercise to conventional lead-acid batteries? 

Thanks. I’ll try that. I only tried the reconditioning mode once (yesterday) as a last gasp effort to save the battery. 
I’ve ordered a new battery today. I’ll do some more voltage checks once the new battery is fitted.

[paulbrown22]

56 minutes ago, drdoom said:

I'd also have a read with voltmeter when the C-TEK is connected. Is it a valid strategy applying a "conditioning" exercise to conventional lead-acid batteries? 

Supposedly yes! Some of the Ctek chargers have a mode to recondition and desulphate the plates in a standard lead acid battery. I've found it pretty good in the past with batteries that are losing capacity, but probably not if they've been pushed completely over voltage for an extended period.

[Rambo]

Agreed.

One of my CTEK's will detect when and if desulphation is required and go into an extra mode.

As you say, if a lead acid battery is dead or has been left discharged for a long period of time, nothing will work.

[GreenGoddess]

My battery has the opposite problem. It’s not dead, it’s more alive than it should be 😂

[Rambo]

Have you got your order in at TAYNA yet?

[GreenGoddess]

16 minutes ago, Rambo said:

Have you got your order in at TAYNA yet?

I was going to use Tanya but I found a better deal elsewhere. £52 delivered for a Hankook battery. 

[Rambo]

What is its Ah (amp hour) rating? Usually the lower the rating the cheaper it is.

I was going to recommend a Varta silver.