12v Battery advice needed (non boaty)

[Plevier]

Plevier, battery was on charge for some 12 hours yesterday. I checked voltage periodically (with charger running and connected to battery) and it was rock steady at 15.4 volts with ammeter on charger showing zero. Battery/charger are in the garage and battery is showing no signs of warming up at all which given earlier comments I am a little surprised at. At this stage I have no idea at all whether it has recovered. I will put it back on the car tomorrow, with the one fuse removed. I will then keep an eye on voltage (no plans to use it for a week or so) and possibly take it back to ATS and ask them to check it again. Whilst their Bosch tester may not be ideal it will give a me a better indication of where I stand than with my kit ( I do have a hydrometer but that's seen better days and as I said previously, battery is "sealed for life" so I will need to carefully ease (break) the top off to even get to the electrolyte.

Thanks for your thoughts and Happy Christmas by the way.

I don't think that's a good sign if you were getting negligible current at 15.4V.
Bit puzzling really. It would suggest the battery is completely utterly dead, probably from being left 100% discharged for quite a long time, but you say (I think) that's not the case.
If you can get some life out of it, then at that voltage it should definitely pass some significant current. Stuck/duff ammeter?
Was it gassing? Even if you couldn't see, you would hear it fizzing quietly with ear against case. If so, there was some current.
Even 12 hrs at that voltage wouldn't lose a lot of water, electrolysis takes a lot of energy. (of course if you genuinely have no current, then no water loss regardless of voltage!)
At least you know you don't have internal shorting - unless the ammeter is stuck/duff.
As annageek said, you'll really only resolve this by a capacity test at 5A current. Difficult to do accurately but you can get an idea with a 60W headlamp bulb, discharging down to 10.5V under load.
Must recharge immediately of course.

PS You call the battery "sealed for life". I take it you mean a "sealed maintenance free" type with liquid electrolyte in, not "sealed lead acid" i.e. AGM/gel/VRLA. If it is actually the latter then there is little you can do.

 

[Pete735]

Plevier,

Interesting morning this morning. Battery was disconnected from charger around 10.00pm 24/12. First thing I did today was put a meter on it to find it was reading 14v, multimeter is a Rapistan digital, a few years old, but to my knowledge a reliable piece of kit. I do not recall ever seeing a battery at 14v before even checking immediately after disconnecting a charger. Anyway, put it on car turned key and starter raced away fired up almost instantly, let it run for 5mins and then turned it off. So battery is not completely dead. Over the next hour I was checking current draw with meter (0.067amps) whilst doing other things. I then checked battery voltage (leads to it disconnected) and had 12.4 volts. Given my 14 volts initially and bear in mind this was 36 hours after coming off charger I think I expected voltage to be higher. I'm not sure if I am any further forward now, but perhaps you know better.

Battery is "Sealed Maintenance Free". Charger is probably 30 years old, an Einhell AFN5 with an analogue ammeter so although it appears to read nothing, we are not talking top quality accuracy I suspect.

We are away for a few days from tomorrow so I will leave battery fitted, but my betting is that if I try it when I get back, engine will fire first time.

Ref headlight bulb and 5amp test. Easy enough to set up, but what do I do exactly? Connect bulb and time how long it takes to discharge down to 10.5 volts? What "time"then constitutes a good/bad/indifferent battery or have I got this wrong?

Thanks for your comments by the way.

 

[Pete735]

gordmac, first thing I did was disconnect the sword and the ikha unit as they are both in the circuit that is causing me trouble. Sadly, disconnection made no difference.

 

[Plevier]

12.4 does sound low.
For discharge test, as battery is nominally 100Ah on 20h it should give 5A for 20 HRs down to (probably) 10,5V, maybe 10.2, standards vary.
To be accurate you need constant current control to correct for voltage drop during discharge, and temperature control at 25 deg C. In the manufacturer's test lab it will all be computerised of course, but a 60W bulb will approximate to it!
If you measure current at intervals and plot it you can integrate for Ah.Normal industrial practice would be to fail it if it didn't achieve 80% capacity which you can approximate to 16 hours.

Plevier,

Interesting morning this morning. Battery was disconnected from charger around 10.00pm 24/12. First thing I did today was put a meter on it to find it was reading 14v, multimeter is a Rapistan digital, a few years old, but to my knowledge a reliable piece of kit. I do not recall ever seeing a battery at 14v before even checking immediately after disconnecting a charger. Anyway, put it on car turned key and starter raced away fired up almost instantly, let it run for 5mins and then turned it off. So battery is not completely dead. Over the next hour I was checking current draw with meter (0.067amps) whilst doing other things. I then checked battery voltage (leads to it disconnected) and had 12.4 volts. Given my 14 volts initially and bear in mind this was 36 hours after coming off charger I think I expected voltage to be higher. I'm not sure if I am any further forward now, but perhaps you know better.

Battery is "Sealed Maintenance Free". Charger is probably 30 years old, an Einhell AFN5 with an analogue ammeter so although it appears to read nothing, we are not talking top quality accuracy I suspect.

We are away for a few days from tomorrow so I will leave battery fitted, but my betting is that if I try it when I get back, engine will fire first time.

Ref headlight bulb and 5amp test. Easy enough to set up, but what do I do exactly? Connect bulb and time how long it takes to discharge down to 10.5 volts? What "time"then constitutes a good/bad/indifferent battery or have I got this wrong?

Thanks for your comments by the way.

 

[annageek]

WHat charger was being used to get the 15.4V with not much current? As Plevier says though, this is not a good sign and suggests impedance.... though it was still OK to start the car with.

The rested OCV (after coming off charger) is normally seen after 3 or 4 hours, so 36 is plenty to let the voltage settle. 14V is high, but batteries with impedance do sometimes settle at higher voltage. Basically, under some circumstances (I'm not sure what - I'm not an electrochemist!) you get a corrosion cell formed in each cell which augments the 2V nominal cell voltage of a LA cell. This would soon drop away with even the tiniest of loads, though, and once the voltage has been dropped, the corrosion cell breaks down, and no longer develops voltage. For this reason, it sort of appears as a kind of 'electrochemical hysteresis' effect, and goes part way to explain why the voltage after running on the car for 5 minutes was 12.4V.

Couple all of that with the fact that your alternator may only be kicking out current at 13.4V or so (by the time its seeing a load) then if you have impedance in the battery, the alternator will just not recharge the battery.

To me, it does seem that you have a sulphated battery, but not so heavily sulphated so as to *just about* crank the car. If it were me, I'd do the following:

1. Check the electrolyte levels on the battery are ok (If not, top up with DI water and recharge with your bench charger).

2. Crank the engine a few times (5 to 10), each time, killing the engine as soon as it starts (to deliberately not recharge the battery) and pause for about 30s between cranks to allow the battery's plates to re-polarise.

3. Crank the engine one more time and leave it to run for a couple of minutes.

4. Recharge the battery using a bench charger for 24 hours or so.

5. Repeat if things still don't seem quite right.

The reason for the cranking is not to deeply discharge the battery (in fact, assuming the car is reasonably easy to start, 5-10 times won't take very much at all out of the battery, in terms of capacity). It's simply to give it a work out, and try to burn off any soft sulphation. At work, we would use a 20 milliohm resistive load in 5 second bursts to perform this task, but unfortunately, its not the sort of thing you find in the kitchen drawer... hence, a loaded starter motor is probably your best bet.

It has two chances... it'll either work or it wont. Given the amount of general 'faffery' involved, I think you'd be forgiven if you didn't even bother too. For me, even if I could get the battery to appear as though it has recovered somewhat, I'd always have it in the back of my mind that the battery was a bit weaker/more likely to fail than it should be, and that'd bug me so much that I'd end up replacing it before long anyway!

 

[Plevier]

Basically, under some circumstances (I'm not sure what - I'm not an electrochemist!) you get a corrosion cell formed in each cell which augments the 2V nominal cell voltage of a LA cell. This would soon drop away with even the tiniest of loads, though, and once the voltage has been dropped, the corrosion cell breaks down, and no longer develops voltage. For this reason, it sort of appears as a kind of 'electrochemical hysteresis' effect, and goes part way to explain why the voltage after running on the car for 5 minutes was 12.4V.

Must admit it didn't twig with me that the 14V was after over a day off charge, I thought it was a few hours. Very odd. However in a good few years with a major battery manufacturer I never heard of the corrosion cell idea and after some head scratching I don't see how it could supplement the terminal voltage. You can get local cells on the plates, particularly with antimony migration and deposition in old high antimony (~10%) types, but all they do is promote gassing and plate corrosion. I don't think they happen to any noticeable extent with modern high purity low antimony or calcium grid alloys.

Convince me! I confess I can't offer an alternative explanation for the 14V.