Battery Top Ups

[Tex]

Having checked my domestic wet cell batteries (2 x 130ahr) I find that once again there is no need to top up the distilled water. The batteries are now five years old and have never shown signs of lower fluid levels. I have my doubts about their ability to hold the charge as well as they should.
Any thoughts, should they now be replaced?

 

[VicS]

Having checked my wet cell batteries (2 x 130ahr) I find that once again there is no need to top up the distilled water. The batteries are now five years old and have never shown signs of lower fluid levels. I have my doubts about their ability to hold the charge as well as they should. Any thoughts, should they now be replaced?

Charge em with a good automatic charger. Aim to charge them to the point at which the voltage is 12.7 ish to 12.8 after resting with no charge or load for 12 hours.

If you cannot get to that level of charge they are probably not much good , but keep trying.

Then monitor the voltage with no further charge or discharge for as long as possible. The volts will fall quickly at first then more slowly. A good battery will take weeks to fall to 12 .5. A really good one may hardly fall at all in that time.

If you have a hydrometer use that to monitor them as they are not sealed.

When they start to need topping up it's a bad sign , unless it's due to overcharging.

They should still be fine after 5 years. I have three cars with batteries around 10 years old although I doubt if one would have got through a severe winter.

 

[TradewindSailor]

These are presumably deep cycle batteries and obviously not maintenance free.

I take issue with the statement "When they start to need topping up it's a bad sign , unless it's due to overcharging." In order to properly charge the battery it is very likely that some of the electrolyte will evaporate. It's not a bad sign at all. In fact it is an indication that the batteries are not being undercharged leading to a possibility of sulphating up. A controlled 'over-charge', also known as a conditioning charge or an equalisation charge is normal procedure for non-sealed batteries ..... 'over-charge' may confuse readers.

 

[sailinglegend420]

.....I take issue with the statement "When they start to need topping up it's a bad sign , unless it's due to overcharging." ....

I agree - if batteries never need topping up they are being undercharged. They must reach their gassing voltage to be properly charged.

 

[nigelmercier]

They must reach their gassing voltage to be properly charged.

... almost ...

 

[sailinglegend420]

... almost ...

No... they must get to their gassing voltage at which point they stir up the electrolyte to prevent stratification, but they don't gas that much to cause water loss. Only when the batteries are FULLY charged will the energy from the charging voltage cause excessive gassing. The current will have gone down to zero but the voltage will do the damage - that is why chargers drop to float voltage. This is "Overcharging a battery".

 

[Tex]

I agree - if batteries never need topping up they are being undercharged. They must reach their gassing voltage to be properly charged.

I wonder about this, the Batteries in question are charged by both shore power mains charger and by alternator. (Not at same time) Surely one of these methods must eventually get them charged properly and cause fluid to need topping up?

 

[GHA]

Only when the batteries are FULLY charged will the energy from the charging voltage cause excessive gassing. The current will have gone down to zero but the voltage will do the damage - that is why chargers drop to float voltage. This is "Overcharging a battery".

That makes no sense??
How can" the energy from the charging voltage" exist without some current? How can watts exist just from volts without amps?
If there is no energy transfer then what causes the gassing?

 

[sailinglegend420]

That makes no sense??
How can" the energy from the charging voltage" exist without some current?

The small current that causes the gassing will probably not show on your Battery Monitor.

Sorry I didn't write a full PHD thesis to fully explain this - you can find a good 17 page report here:

http://www.battcon.com/PapersFinal2008/ODonnellPaper2008PROOF_6.pdf

To keep it very simple, the "current" actually charging the battery falls to zero and the excess voltage causes a small current to electrolyse the water in the electrolyte mix of sulphuric acid and water, causing free hydrogen and oxygen to be vented from the battery.

 

[GHA]

The small current that causes the gassing will probably not show on your Battery Monitor.

Sorry I didn't write a full PHD thesis to fully explain this - you can find a good 17 page report here:

http://www.battcon.com/PapersFinal2008/ODonnellPaper2008PROOF_6.pdf

To keep it very simple, the "current" actually charging the battery falls to zero and the excess voltage causes a small current to electrolyse the water in the electrolyte mix of sulphuric acid and water, causing free hydrogen and oxygen to be vented from the battery.

That makes a bit more sense now, previous post was quite misleading getting energy from voltage alone.

If there is any gassing at all going on my meter will show the current.

 

[charles_reed]

In practice, to attain maximum battery capacity, it is necessary to take and hold them @ just gassing point - hence the provision on smart chargers of an "equalising" period.

It does beg two points:- 1. whether those last few Ah are worth the probability of battery damage. 2. Why it is not a commonly acknowledged fact that ONLY open lead acid cells (which permit topping up) are the only batteries it's possible to fully charge?

I, personally, view it as very similar to the divisive argument which rent the 18/19th century church as to the precise number of angels that could dance on the head of a pin.

In response to the OP, It's probable that your batteries have never been fully charged and would benefit from an exercise in de-sulphation. They might be near the end of their life @ 5 years but I've had 10 years out of a Lucas (domestic) traction battery. I certainly would not throw them away willy-nilly.
The Trojan site had instructions on how to "service" batteries which involved two cycles of full discharge, interspersed with a period of charging with what sounded very like a de-sulphation cycle. They suggested this be done every 18-24 months of use.

Trojan batteries were, then, considerably better made than most normal commercial batteries, and only available in 6v units.
Bill Cooper reckoned to get 25 years out of his Fe/acid batteries and persisted with them despite the drone of august opinion that considered him ill-advised.

 

[vyv_cox]

My 3 x open cell batteries were charged by 125 watts of solar panel and the engine via Sterling alternator regulator when running. Over a season I might well have added 4 litres of de-ionised water in total to them. This is in line with the Sterling info. I now have closed cell batteries that are entering their fourth season, apparently all OK, with the Sterling setting adjusted accordingly.

 

[charles_reed]

My 3 x open cell batteries were charged by 125 watts of solar panel and the engine via Sterling alternator regulator when running. Over a season I might well have added 4 litres of de-ionised water in total to them. This is in line with the Sterling info. I now have closed cell batteries that are entering their fourth season, apparently all OK, with the Sterling setting adjusted accordingly.

Of course, Vyv, Charles Stirling is of the school that considers only open cell batteries are worth having, and definitely boils them gently on the equalising charge.
That's a major problem with his mains chargers left on for any time - any break in supply and they merrily indulge themselves in another round of 4hrs @ 14.7V (or thereabouts).

 

[GHA]

In practice, to attain maximum battery capacity, it is necessary to take and hold them @ just gassing point - hence the provision on smart chargers of an "equalising" period.

???

An equalising voltage is a long way past the voltage at which gassing will start.

More aggressive charging might well be unanswerable, do you crank up the voltage when the sun's out to get close to a full charge in there at the risk of wear on the battery or back it off with the chance of not getting a full charge in there, and risk some sulphation.....

I tend towards the latter. Though means a bit more watering.

(also bearing in mind, batteries are processes, not black and white devices, fully charged doesn't really exist.)

 

[sailinglegend420]

....It does beg two points:- 1. whether those last few Ah are worth the probability of battery damage. 2. Why it is not a commonly acknowledged fact that ONLY open lead acid cells (which permit topping up) are the only batteries it's possible to fully charge?...

The last few Ah are done at a FLOAT voltage which is well below the battery gassing voltage - if temperature corrected properly - so ALL batteries can eventually be fully charged.

If you don't regularly fully, 100%, fully charge they sulfate and die early.

 

[charles_reed]

The last few Ah are done at a FLOAT voltage which is well below the battery gassing voltage - if temperature corrected properly - so ALL batteries can eventually be fully charged.

If you don't regularly fully, 100%, fully charge they sulfate and die early.

The first is an engagingly simple theory, with which I was brought up, and now appears to have been amended.

As to #2 I'd ask whether it was your opinion or based in fact? Certainly Trojan's advice appeared to be based on the hypothesis that no-one, ever, fully charged their batteries, hence the recommendation to fully discharge and briskly, fully recharge their cells under controlled conditions.

 

[sailinglegend420]

The first is an engagingly simple theory, with which I was brought up, and now appears to have been amended.

What I said was they will eventually get fully charged in FLOAT, everybody thinks that they ARE fully charged when they switch to FLOAT.

As to #2 I'd ask whether it was your opinion or based in fact? Certainly Trojan's advice appeared to be based on the hypothesis that no-one, ever, fully charged their batteries, hence the recommendation to fully discharge and briskly, fully recharge their cells under controlled conditions.

Every battery manufacturer gives the same advice - if you don't FULLY charge batteries at least one a month they sulphate - fact, not opinion. As part of the chemical process Lead Sulfate forms on the plates and has to be turned back to Lead and Sulfuric acid on recharge (simple explanation). The problem is the lead Sulfate crystals harden after a few weeks and even equalization at 15.5 volts won't shift them. So each time you don't FULLY recharge them a little bit more Lead Sulfate gets left behind and reduces the capacity of the battery.

So where is the link to Trojan's advice? I would agree that most people never get their batteries fully charged, unless on shore power for 24 hours or more.

There is a theory that batteries can never be fully charged because of their coulombic efficiency which gets less and less as the battery charges. This is quoted as between 75% and 98% depending on the type of battery. This is very non linear, at less than 50% State of Charge, SoC, the efficiency is nearly 100%, at 100% SoC the efficiency is very low. At 85% SoC the efficiency is at 50%, which means if you put in 10Ah then only 5Ah get absorbed by the battery, and as you approach 99% the coulombic efficiency makes it harder to put Ah into the battery. Coulombic efficiency is different to the Charge Acceptance Rate which means the current the battery will take gets less and less as your SoC gets closer to 100%,

So two factors are fighting against you as you try to charge, which is why the average solar array has a hard job getting a bank to 100%. So if you think your batteries are fully charged by lunchtime - think again.

 

[charles_reed]

What I said was they will eventually get fully charged in FLOAT, everybody thinks that they ARE fully charged when they switch to FLOAT.




So where is the link to Trojan's advice? I would agree that most people never get their batteries fully charged, unless on shore power for 24 hours or more.

Unfortunately the website has been extensively rebuilt and the original is no more - however if you care to search through setsail.com you'll find a blog by Steve Dashew detailing the process and the improvement he claimed in battery capacity.


So two factors are fighting against you as you try to charge, which is why the average solar array has a hard job getting a bank to 100%. So if you think your batteries are fully charged by lunchtime - think again.

Does anyone ever expect to fully charge their batteries on solar - I've got 328 watts, in Greece, never expect to get there and have never been disappointed.

As a rough rule of thumb (for my system) 8 hours on motor (with a 110 amp alternator and smart charger) or 48 hours on shorepower charging (20 amp, 4hrs equalising @ 14.4v); all into about 330Ah.
There are as many theories as experts out there and we all have to find out what works for us.

 

[Tex]

Update from OP.
I have checked batteries after 6 days without any charge or draw.
Together the bank measures 12.55. One battery records 12.55 but the other only 11.9V.

Suggestions please, should I replace one, both, neither?

 

[GHA]

Update from OP.
I have checked batteries after 6 days without any charge or draw.
Together the bank measures 12.55. One battery records 12.55 but the other only 11.9V.

Suggestions please, should I replace one, both, neither?

If they're five years old then might as well bite the bullet and do both. One has gone, the other probably isn't far behind.