A different battery question...

[Smelly]

A lot of batteries have little indicators that tell us whether they're charged or not. I'm interested in how they work, but more to the point I'm trying to find out in what circumstances they do, or do not indicate battery failure.

 

My mulitmeter battery's just run out (and it's gone dark now) so this can stand as a curio 'til I can get to the battery shop tomorrow. Hopefully it can stay that way as well!

 

Ta!

 

[dor]

I was intrigued by these whe I first saw them. I came to the conclusion that it is a little plastic ball with a very specific density. When the battery is charged the ball floats and shows green. I wondered initially if there was a little led in there, but decided it relied just on reflected light.

[Smelly]

I was intrigued by these whe I first saw them. I came to the conclusion that it is a little plastic ball with a very specific density. When the battery is charged the ball floats and shows green. I wondered initially if there was a little led in there, but decided it relied just on reflected light.

 

And here was me wondering whether it was a chemical thing...

[MikeV]

And here was me wondering whether it was a chemical thing...

It is a chemical thing combined with a physical thing. The chemistry of fully charged battery electrolyte is such that it's specific density is higher and the little green ball floats. If it's "not green" I suspect your battery is already damaged, but I don't actually know at what discharge the little green ball sinks.

 

I do know it tells you nothing about the condition of the battery as I had a bow thruster battery that showed green but couldn't deliver any meaningful amps to the BT even after a full charge. I've never seen a "not green" indication on my battereries but then I never let them go below 50% charge.

[Guest]

My previous batteries were still showing a healthy green indicator when completely knackered. A gimmic I'm afraid.

[Smelly]

I do know it tells you nothing about the condition of the battery as I had a bow thruster battery that showed green but couldn't deliver any meaningful amps to the BT even after a full charge. I've never seen a "not green" indication on my battereries but then I never let them go below 50% charge.

 

So, working on a little green ball hypothesis... As the batterey hydromter thinks the batts are knackered at a low electrolyte SG, then if the ball's still floating, i.e high SG then there's plenty of sulphur in the electrolyte and not too much sticking to the plates...?? Or if the batteries knackered then it'd indicate a shorted cell or similar?

 

I assume the little green ball only shows the condition of 1 cell so another one could have had it and we'd know no different?

[Guest]

So, working on a little green ball hypothesis... As the batterey hydromter thinks the batts are knackered at a low electrolyte SG, then if the ball's still floating, i.e high SG then there's plenty of sulphur in the electrolyte and not too much sticking to the plates...?? Or if the batteries knackered then it'd indicate a shorted cell or similar?

I assume the little green ball only shows the condition of 1 cell so another one could have had it and we'd know no different?

Yes one cell only.

[Pretty Funked Up]

My previous batteries were still showing a healthy green indicator when completely knackered. A gimmic I'm afraid.

 

Yes Ive had this happen quite a few times now... I think our little green floaty friend gets stuck at the top

[chris w]

Yes one cell only.

That's why a battery can look good (as judged by the green indicator) but actually can have a damaged cell which effectively makes the battery crap. So, in actuality, the green ball only actually tells you that that particular cell is OK not that the whole battery is OK.

 

Chris

[Smelly]

Well, matey in question borrowed my hydrometer a while back so this might present the chance to get it back

[alan_fincher]

We've had the reverse to what some are describing.

 

All cells measured on a hydrometer indicate a near fully charged battery. battery voltage agrees this.

 

Absolutely no sign of the green balls.

 

Not useful, it seems.

[Sir Nibble]

I've taken one or two of these to bits. There are two balls, one green and the other usually yellow. They operate as a sort of flint axe hydrometer and as catty says monitor one cell only. I believe they were designed in when sealed batteries arrived as a sop to luddite professionals like me who thought the world would end if we couldn't use a hydrometer. They are indicators only and of little practical use, and yes I am sure that battery monitoring and diagnosis is far easier when the vent caps can be removed and the cells "dipped" with a hydrometer.

[Smelly]

I've taken one or two of these to bits. There are two balls, one green and the other usually yellow. They operate as a sort of flint axe hydrometer and as catty says monitor one cell only. I believe they were designed in when sealed batteries arrived as a sop to luddite professionals like me who thought the world would end if we couldn't use a hydrometer. They are indicators only and of little practical use, and yes I am sure that battery monitoring and diagnosis is far easier when the vent caps can be removed and the cells "dipped" with a hydrometer.

 

Results to follow then!

[jelunga]

I totally agree. I thought it was a bad day when car batteries no longer had exposed cell straps, so if one cell went in "in the old days" you could link across and put that cell out of circuit effectively. Then maybe get a nominal 10 v that might start the engine. Unless of course you had a Morris 8 with 6 volt electrics, or was that the early Minor?

 

Can not remember.

 

I've taken one or two of these to bits. There are two balls, one green and the other usually yellow. They operate as a sort of flint axe hydrometer and as catty says monitor one cell only. I believe they were designed in when sealed batteries arrived as a sop to luddite professionals like me who thought the world would end if we couldn't use a hydrometer. They are indicators only and of little practical use, and yes I am sure that battery monitoring and diagnosis is far easier when the vent caps can be removed and the cells "dipped" with a hydrometer.

[Gibbo]

Yes they work exactly as described. They float up to become visible when the SG reaches "fully charged". Some of them have 2 or 3 balls which swap places in a sloping groove. The one just floating is the one that is visible.

 

But as others have pointed out they only show that one cell. If it's green (but see below) then that cell has good SG and therefore must be fully charged and must be in reasonable condition (ie not sulphated) otherwise the sulphate would be stuck to the plates and there wouldn't be enough in the electrolyte to float the ball.

 

One of the other cells could be completely knackered.

 

But, after a few years the ball gets a coating of sulphate on it and it then sticks in its little channel. This is why even a flat cell can sometimes show green or a fully charged cell can show empty. It depends where the ball sticks.

 

Further, if the electrolyte level is low then the ball may not show even when fully charged.

 

Gibbo

[Smelly]

So even our balls get sulphated

[NB Alnwick]

Yes they work exactly as described. They float up to become visible when the SG reaches "fully charged". Some of them have 2 or 3 balls which swap places in a sloping groove. The one just floating is the one that is visible.

 

But as others have pointed out they only show that one cell. If it's green (but see below) then that cell has good SG and therefore must be fully charged and must be in reasonable condition (ie not sulphated) otherwise the sulphate would be stuck to the plates and there wouldn't be enough in the electrolyte to float the ball.

 

One of the other cells could be completely knackered.

 

But, after a few years the ball gets a coating of sulphate on it and it then sticks in its little channel. This is why even a flat cell can sometimes show green or a fully charged cell can show empty. It depends where the ball sticks.

 

Further, if the electrolyte level is low then the ball may not show even when fully charged.

 

Gibbo

 

Unfortunately, sealed batteries with these gimmicks seem to be the fashion just now (and possibly have been for the last few years) but it worries me when using these as cabin batteries.

With the traditional open cells, I have always needed to keep an eye on them and, especially in the summer (the batteries are in the engine room) they have required frequent topping-up. It will be interesting to see how my new batteries, which cannot be topped up, cope with the variations in temperature and load.

[kevinw]

I totally agree. I thought it was a bad day when car batteries no longer had exposed cell straps, so if one cell went in "in the old days" you could link across and put that cell out of circuit effectively. Then maybe get a nominal 10 v that might start the engine. Unless of course you had a Morris 8 with 6 volt electrics, or was that the early Minor?

 

Can not remember.

 

That would be a Morris 8. My father had one and he used to start it with a set of U2 batteries (D cells, in today's parlance, I think) between the SW connection on the coil and the positive (earth) of the battery and then turn the engine over on the starting handle. Very hit and miss.

 

Kevin

[AccordGuy]

Depends on the maker of the battery but the green eye (according to the maker of such things, ITW Delpro if you want to Google them) can be bought with 11 different "green eye on" SG ratings. This is to take into account of different battery designs and usually should equate to the battery being "more than 65% charged", not "fully charged". So it's not safe to say that because you can see the green eye that the battery is ok. Prolonged storage or cycling at 70% charge will damage the battery just the same.

 

Solar installations are particularly prone to this as they get run down at night and it may take a few days of partly cloudy weather before the battery recovers enough charge to be fully charged. Plus, there's the tendency to design the battery bank to be somewhat over-sized so that solar energy is not wasted by having too small a battery that gets quickly full and then the remainder of the days solar energy is wasted.

 

Once in a while (ideally, at least once a week) the battery should reach fully charged and maybe once a month it should be equalised (over-charged slightly) to even out any weak cells. Some types (gel & AGM) can't be equalised though as they lose too much water and die or would explode from the internal gas pressure.

 

Maybe the only useful thing the eye shows is when the battery needs topping up. The eye goes bright crystal clear when the level of electrolyte in the cell has dropped below the level of the float chamber on the thing. Again, they sell different length thingys so the battery manufacturer can decide what is the right minimum electrolyte level. On a sealed for life battery that's bad news because you can't top them up... new battery time. On a vented battery you might check the charge termination settings if the battery is gassing too much and losing water at an unacceptable rate.

[Smelly]

Depends on the maker of the battery but the green eye (according to the maker of such things, ITW Delpro if you want to Google them) can be bought with 11 different "green eye on" SG ratings. This is to take into account of different battery designs and usually should equate to the battery being "more than 65% charged", not "fully charged". So it's not safe to say that because you can see the green eye that the battery is ok. Prolonged storage or cycling at 70% charge will damage the battery just the same.

 

Solar installations are particularly prone to this as they get run down at night and it may take a few days of partly cloudy weather before the battery recovers enough charge to be fully charged. Plus, there's the tendency to design the battery bank to be somewhat over-sized so that solar energy is not wasted by having too small a battery that gets quickly full and then the remainder of the days solar energy is wasted.

 

Once in a while (ideally, at least once a week) the battery should reach fully charged and maybe once a month it should be equalised (over-charged slightly) to even out any weak cells. Some types (gel & AGM) can't be equalised though as they lose too much water and die or would explode from the internal gas pressure.

 

Maybe the only useful thing the eye shows is when the battery needs topping up. The eye goes bright crystal clear when the level of electrolyte in the cell has dropped below the level of the float chamber on the thing. Again, they sell different length thingys so the battery manufacturer can decide what is the right minimum electrolyte level. On a sealed for life battery that's bad news because you can't top them up... new battery time. On a vented battery you might check the charge termination settings if the battery is gassing too much and losing water at an unacceptable rate.

 

thank you and welcome...

 

you know after posting this I never did buy that battery for my multimeter, however his having a good case of diesel bug which stopped his engine dead the day after I became somewhat distracted helping him fix both that and the leaking fuel line