Problems with flat battery

The quality is certainly variable, but I don't mind too much personally, given the price.

The reason their cheap voltmeters are accurate is not because of any special endeavours by the Chinese manufacturer. It's because the whole voltmeter (pretty much) is pre-built in silicon. It's not far wrong to say that it would cost the manufacturer more to make an inaccurate one than it does to make an accurate one - because the accuracy is built in on chip.

brodco wrote:Hi  

Weedaf wrote: how do they do goods at that price?

-mojo- wrote: production costs in China are ultra-low because they make millions of them to the lowest quality standards that they can get away with

Agreed up to a point,  that’s often true but not always.

The Chinese can produce high products an an unbelievably low price. After all the likes of Apple and others get their products made in China.



I’ve found Chinese quality variable. I’ve seen some very good and some incredibly bad quality and downright dangerous items. Problem is it can be difficult to tell which is which.

There are two concerns main I have with have with products from China:

1) is it going to electrocute me?
2) Is it going to catch fire?

I purchased five of these cigar lighter voltage meters and I have to say they were remarkably good for the price.  Clearly the electrocution possibility is not a concern and they were well fused so I’m confident they won’t catch fire.
I decided to check the accuracy of my particular examples and the worst of them was 0.03V in error.  Not perfect but perfectly adequate for the purpose a product like is likely to be used for.



Of course that’s only a random sample and so can’t necessarily be extended to all of them!

I have one of these and it reads  0.3V low at 12V so when the display reads 12V the battery is actually 12.3v
At 15 volts its spot on.

I have been amazed at what I have learnt from having my battery problem. Looks like purchasing one of these will at least give me peace of mind of the health of my battery.
I also learned that a leisure battery is a different 'animal' which will recharge after being flat.
Thanks for all this info, I hope it is useful for other members too.

Weedaf wrote:
I also learned that a leisure battery is a different 'animal' which will recharge after being flat.

Unfortunately it's more complicated than that! There are different types of leisure battery - some cheap (roughly comparable in cost to engine batteries) and some very expensive.

As a general rule, the cheap ones will handle complete discharge hardly any better than engine batteries. Generally, it's only the very expensive ones that will tolerate being completely discharged repeatedly. There are several types of the latter - the expensive (in the range £150-250) are typically AGM batteries, and the very very expensive ones (in the range £200-500) now tend to be lithium ion based.

Mostly, people fit the cheap ones, which are just conventional lead-acid batteries - like engine batteries but with a slightly different internal structure.

Hi

spanner wrote:I have one of these and it reads  0.3V low at 12V so when the display reads 12V the battery is actually 12.3v
At 15 volts its spot on.

brodco wrote:I decided to check the accuracy of my particular examples and the worst of them was 0.03V in error.

Opps sorry that's a typo I meant to say 0.3V (too late to edit now).

Brod

-mojo- wrote:

Weedaf wrote:
I also learned that a leisure battery is a different 'animal' which will recharge after being flat.

Unfortunately it's more complicated than that! There are different types of leisure battery - some cheap (roughly comparable in cost to engine batteries) and some very expensive.

As a general rule, the cheap ones will handle complete discharge hardly any better than engine batteries. Generally, it's only the very expensive ones that will tolerate being completely discharged repeatedly. There are several types of the latter - the expensive (in the range £150-250) are typically AGM batteries, and the very very expensive ones (in the range £200-500) now tend to be lithium ion based.

Mostly, people fit the cheap ones, which are just conventional lead-acid batteries - like engine batteries but with a slightly different internal structure.

Off topic slightly, (sorry), but you may be interested in how resilient a 12V battery can be, (I'm sure that you already know this mojo, but others may not).

My car has recently had (what turned out to be) an alternator problem.
One day in Feb, a hundred miles from home on the M5, I started to get cascades of warning messages and as I left the motorway, the power steering packed in.
When I arrived at the customer's works the auto gearbox locked up and the engine stalled.
The battery was down at 10.6V. Measuring the alternator output, I found that it was OK so assumed that there was a cell fault in the battery and went and bought a new one.
I also bought a plug in voltmeter like those being discussed to keep an eye on things in case it was in fact the alternator.

Once I was home, I put the old battery on an intelligent charger and it came back up to normal, and retained a good charge after several weeks of standing. "That's good" thinks I.

The car then behaved itself for nearly three months...

Earlier this month, I got the same problem back (with the new battery in the car) and was able to nurse the car home with a completely failed alternator, (as I didn't fancy sitting in the freezing cold on the moors waiting for the RAC).

When I got home, the new battery was at 8.5V "That's a goner now", thinks I, but I took it out and put it on the intellicharger.

In the meantime, I took the old (but still fully charged after its hammering) battery, installed it in the car and then drove the 20 miles to the nearest specialist for my vehicle where I had a new alternator the same day.
When I got to the specialist, the battery voltage was about 11.6V, not bad considering it had been powering the steering, gearbox and lights with no alternator output.

The new battery has also recovered, after about a week on the charger, and is back in the car, which starts very easily at a good cranking speed (it's diesel BTW).

I'm pretty sure that both batteries are more or less fine, even after being battered into submission at 8.5V in the case of the new one.

Just saying, it's not a given that seriously discharging a 12V car battery is going to necessarily destroy it, although I wouldn't do it out of choice.
It's always worth seeing whether it has survived in a usable state.

Awaits incoming

meanchris wrote:it's not a given that seriously discharging a 12V car battery is going to necessarily destroy it

Indeed - as far as I can tell, you tend to get the worst outcome if it's discharged and then left discharged for more than a short time. Once it's discharged, lead sulphate deposits start to form on the plates, and these get thicker with time. The thicker they get, the more difficult it is to clear them. Charging the battery should (in theory) do it, but the problem is that they don't dissipate evenly, so the capacity is reduced anywhere that there are remnants. So recharging immediately will certainly help.

The other two main detrimental effects are gassing and physical distortion of the plates - but they only usually happen during high rates of discharge and charge.

And then sometimes the plates themselves are not very well made, and vibration alone can cause bits to drop off and short out to adjacent plates - though on some types they put fabric or other types of packaging around the plates to contain this.

Despite the fact that they are precision-made components, there still seems to be a lot of variability in batteries - sometimes you will get good ones, and sometimes they won't be so good, even sticking to the same make. Life is only going to get more complicated when the non-lead/acid types (LiIon, LiPol, etc) become more common, because they will have completely different characteristics than any of the types that are used commonly today...

-mojo- wrote:
Indeed - as far as I can tell, you tend to get the worst outcome if it's discharged and then left discharged for more than a short time.

I agree, that has been my experience too, though I should also say that I've had some success in my youth with apparently totally dead batteries, by putting a tablet of Bat Aid in each cell and topping them up.

Hi, thank you for all the replies & info. It started last time I tried, I'll maybe get a battery master fitted.