Post Number: 40
|Posted on Friday, 01 August, 2008 - 00:01: |
As an offshoot from the recent posts about getting power back again to unlock a boot I have been wondering about the "maintenance free" aspect of modern batteries.
Being in my 94th year myself and with the battery being in it's 8th I have recently fitted a new battery and had a look at the old one. It is prominently labelled Maintenance Free but it is possible to prise off the covers on the cells and see what the acid level is. When it was new (and I was younger) I checked the acid level in all of the cells and the gravity, All was OK. Three years later I had another look, found the acid levels rather low and topped up. Then, when the new battery was fitted, I had another look. Most of the cells were quite dry and, as a matter of interest I topped them up. The cell at the negative end of the battery took 37cc to bring the level to just over the top of the plates and the next cells (in order from the negative end) took 55cc,86cc,95cc,100cc and 115cc.
This seems to suggest to me that the "maintenance free" is largely sales patter. What have others found?
Post Number: 186
|Posted on Friday, 01 August, 2008 - 00:21: |
Laurie, It usually means that it's made so that it can't be maintained
Another casualty of our disposable society!
I think the materials are supposed to gas less and the modern charging systems are supposed to keep a battery cooler, leading to less loss and evaporation. Of course any hot weather or fast charging and off the fluid goes!
I always top up where possible.
Post Number: 817
|Posted on Friday, 01 August, 2008 - 12:05: |
Hi Laurie & Paul,
Being somewhat sceptical of marketing claims in relation to automotive products; I always buy the conventional battery with individual caps for top-up purposes. They have the advantage of being cheaper and certainly no problem with availablity so they have not been superceded by the maintenance-free version.
If my memory is correct, the plates in a conventional battery are made from a lead alloy containing a small amount of antimony to strengthen the lead to control buckling in use. The antimony acts as a catalyst for electrolysis of the sulphuric acid electrolyte which reduces the volume over time necessitating the top-up with water.
The antimony is not used in maintenance-free batteries so the electrolysis is significantly reduced but not eliminated entirely and this is why your battery needed topping up. I suspect the same alloy is being used in my "conventional" batteries as I have experienced an increasing number of "dead cell" failures caused by plate buckling and I certainly do not have to top-up as frequently as I did in the past.
It seems to me the main determinant of battery life today is the standard of roads you drive on - the smoother the road; the longer the battery lasts. My 4WD batteries last approximately 3 years before failing.
Post Number: 998
|Posted on Friday, 01 August, 2008 - 12:12: |
Longivity is clearly one of your aims in life but you are game to apply it to car batteries. I get my battery checked regularly and particularly at the onset of Winter. Other times I get it checked as often as I can ask for a decent cup of coffee since I pass my battery man every working day!
That said if he so much as makes a little moue when checking the thing and is anywhere near three years old, its out and in with a new one. These cars are far to heavy to push!
One problem I have had is the occasional car with these new fangled calcium batteries. When they get flattened they need a Hell of an input to get them started on a recharge or else left to my small charger for a couple of days before they will move. I suppose that is progress!
Post Number: 190
|Posted on Friday, 01 August, 2008 - 17:01: |
Hmmmm Bill, just posted on the boot lock thread. I will have to check to see if it is a calcium one and leave it on charge longer.
R-R here fit A/C Delco or Delphi (as they now call them in Europe ) which are sealed but with the floating ball. The amount of dead batteries with 'happy' green balls makes me laugh.
Not allowing them to go flat is always good for longevity. Some batteries seem to never recover from going flat ( Lucas and Varta seemed bad for this ) A/C Delco didn't seem to mind. Perhaps that is why R-R switched?
Trevor P Hodgkinson
Post Number: 15
|Posted on Thursday, 07 August, 2008 - 01:45: |
The metallurgy of the "maintenance free" battery is quite different to a standard battery.
The old battery used to be made from pure lead & lead-antimony .
The antimony is what causes gassing to occur prematurely and is also a big problem in the scrap pool due to the production of stibene gas which is extremely toxic.
Avaition batteries used lead & lead-silver with the electrolyte suspended in a fiberglass matt but the early variants were way down on capacity.
The next developement was the lead & lead -calcium cells which suppressed the beginning of gassing but did not prevent it.
These were the famous exploding sealed batteries of the early 70's.
Now with the advancements in spectrochemicial techniques and the wider use of electron microscopy a whole new series of "micro alloys " have come into vogue.
These typically would be pure lead with less than 2% wt of alloying metals and they have been found to be quite superiour to the previous alloys which could be any thing up to 10% of alloying element,
With such fine controls in the chemistry of the cells, silly little things like the quality of the water being used suddenly become quite critical so the need to seal the batteries.
Most modern batteries will not boil due to reasonable over voltage ( up to around 20 V for a standard 12 V battery ) but the electrolyte will slowly evaporate so the level will drop.
The good news is that they will work better 1/2 full than the old ones did completely full.
Those of you as old as me will remember the old heavy duty , 12 13, 14, & 15 plate batteries that you needed 2 strong men to fit.
Now days I can get 900+ CCA out of a battery that I can easily lift with one hand ( OK with my good hand ).
When I started we used to cast battery grids 3mm thick for standard batteries & up to 6mm for heavy duty ones.
Now days the plates would be in the order of 0.4mm thick & contary to popular belief the thinner the plates the better the battery performance in all aspect except resistance to mechanical vibrations which should not be a problem in anything that came out of Crew but dose give me grief with my old Pommie motorcycles.
Such thin plates are prone to warpage& breakage if not supported with matting and seperator plates which is another good reason for fitting sealed batteries.
I use only the spiral wound cells in everything, the wedding cars my work van & the bikes ( when I can get one to fit) they are 500% improvement on the flat cell designs as the plates being would up ( like a big capicitor) can not warp.
The other big big change has been the depth of the paste & the bonding agent used in the pastes.
Modern batteries have a very thin paste layer so once you have allowed the surface to passivate ( by leaving it flat) then it is "all over red rover" for that battery and the bonding agents which are a really complex organic compound will react with air so it is not good to let them dry out.
Impurities in the water particularly copper, iron, calcium & magnesium will also have an adverse affect on the now quite finely balanced chemistry inside your battery so the use of either demineralised or distilled water is a very good idea if you have a battery designed to be topped up. It is not like the old days when you could give a deaden a wash out with EDTA and overcharge & bung it back in for another couple of years.
And by the way , the lead acid battery is the only automotive part that is commercially viable to be 100% recycled.
Trevor P Hodgkinson
Post Number: 16
|Posted on Thursday, 07 August, 2008 - 01:56: |
If you are wondering, the brand name of the batteries that I use is Optima, which just happens to be the brand that both Arcus auto electricians stock & is also available from Battery World outlets in Australia ( NSW at least) .
The other big advantage is that they do not self discharge so that you can leave them in a car that is not being used for several months & still have enough poke to kick the 6.7 into life.
The bad news is that they are a little taller than the standard battery so while they do fit into the battery bay, there is not enough space left for the tool tray, which is no problem for me as none of my cars had one when I got them.
Post Number: 41
|Posted on Thursday, 07 August, 2008 - 02:00: |
So the electrolyte does slowly evaporate and the level will drop. If it is possible to get access to a maintenance free cell is it a good thing to top up with distilled water or is it better to just leave it alone?
Trevor P Hodgkinson
Post Number: 17
|Posted on Friday, 08 August, 2008 - 08:46: |
Yes it will drop with time elevated temperatures and particularly heavy charging ( well heavy overcharging really ).
We tested a lot in a drying oven at 80 Deg C it would take 3-5 years for the electrolyte to drop to a level where the sealed battery would no longer be able to crank over the engine.
All batteries have to be able to vent or they will explode but most use some sort of one way valve for this purpose so it dose slow down the evaporation quite a lot.
If you can access the cells without destroying the venting system then yes do top it up but you really must use distilled water and better still to use BP ( medical) grade water rather than commercial grade water as the latter is distilled & concentrated in copper and actually has a lot of copper dissolved in it.
The former is a lot more expensive because it is processed in glass so ends up with a Cu content of < 1: 10,000,000.
Unsealed batteries tested in the same way would evaporate their electrolyte in 1-3 years. There was a big difference between brands & with the same brand and case battery type.
Also be aware that if there is evidence that you have opened a sealed battery it's extended warranty will be null & void.
You are more likely to do more damage forcing it open than the dropping electrolyte will cause so I would suggest that you test what you are going to do on an old dead one first.
Also a lot of the new sealed batteries carry the electrolyte in a membrane ( usually fibreglass matting, but some have gone to teflon matting ) so you will not be able to see much.
We did our determinations based on the reduction in weight so we did have not rip open the battery cases till after the testing was finished.
Now to be honest it was not a big test as there was never enough money available & we had to hide the battery purchases in the general lab budget but we had to have some sort of a comparison between what we were making & what was out there, so from a purely statistical point of view our results had a < 10% certainty factor ( that comes from probability tables used in quality control, you need to do 1476 tests to get 99.99 % )
Post Number: 42
|Posted on Friday, 08 August, 2008 - 10:20: |
Thanks for the most interesting info. How does the (fully charged) gravity of the acid change as the evaporation progresses? Does it go much above the 1.280 level which I usually find with a new battery or does it tend to go down as the plates tend to sulphate?
I like your comments about variations between brands etc. I have some rather similar data about mileage from tyres on my MK VI which I must post sometime (covering about 12 sets in nearly 49 years)
Trevor P Hodgkinson
Post Number: 18
|Posted on Friday, 08 August, 2008 - 22:26: |
I know that this will sound strange but the SG dose not change due to the evaporation of water from the electrolyte.
The amount of paste that is involved in the chemical reaction goes down due to the lack of free ions in the electrolyte and thus the capacity of the battery decreases that is the actual amp hours so you have what appears to be a fully charged battery but it will only turn over the motor for 10 minutes instead of 20.
We used to have over 20 different battery factories in Australia but only 3 foundries casting plates.
Much like the Pommie car industry with 25 different marques all assembling different cars with the same basic set of bought in componants.
I always have a laugh that the car makers force the battery makers to produce batteries that are way too frail in order to save about 0.5 kg then add 50 kg in unnecessary electric motors