Recovering a Lead Acid battery after it has been deeply discharged

[T1 Terry]

There have been a lot of threads about flat 12V aux batteries and a bit of mythical knowledge coming from the dealers and most definitely from who ever wrote the 12V maintenance software .... clueless comes to mind .....

A bit of preamble from another thread here Replacement 12V auxiliary battery for MGS5 .... so if you have already suffered through that, you can skip through to the next bit ... or look for something that won't bore you to tears or send you to sleep.

A lead acid battery needs to remain at charging voltage, above 13.6v min, to actually recharge. 13 .6v will maintain the charge at 100% if it is already at 100%, it will bring a battery up to about 50% SOC if it stays at that voltage for 24 hrs or more, but that is no enough voltage to over come the inherent internal resistance of any type of lead acid battery.

Now, if the battery was not saturation charged when built, it will already begin sulphating ..... within 12 hrs actually .....

If the terminal voltage is held at 14V for 12 hrs or more, you can get closer to fully charged, as long as the plates are not sulphated. Once the sulphation starts on lead acid plates, no chemical reaction can occur in that part of the active plate, so capacity is lost.

The only way to remove sulphation is with a pulse charge, higher than 16.5v but very short bursts. This forms very small bubbles within the lead plate that gradually push the sulphur out of the lead ..... As long as it hasn't been there for too long, it will return to the electrolyte and increase the specific gravity of the sulphuric acid ..... if it has been there long enough to bind with the surface of the lead plate, it will flake off and drop to the bottom of the cell electrolyte reservoir ... harmless until it build up enough to reach the bottom of the plates, then it shorts the plates out and you get that sudden dead cell ......

Naturally, this reconditioning pulse charging can't happen when the terminals are connected to any appliance, this includes the vehicle's 12V system, so the battery at minimum must have the negative terminal disconnected. ... I'll explain in another post why the negative terminal should be the first off and the last connected at the end ... If I remember

There are a few quality chargers that can have a reconditioning or de-sulphation cycle engaged, it takes quite a while, the longer it has been sulphated, the longer it will take to de-sulphate .......
C-Tek is a well known brand that has a de-sulphating cycle, you can buy or even build your own, this came up on Google search How to Restore Sulfated Batteries | Battery Chargers but I am not in anyway endorsing them, I've never used any of their products, but there are heaps out there .....

T1 Terry

 

[Black estate]

Yep my brother has a battery reconditioner charger and when I got my MG5 I took the 12V bat off and done it and it's good as gold now.

 

[stevedee]

There have been a lot of threads about flat 12v aux batteries and a bit of mythical knowledge coming from the dealers and most definitely from who ever wrote the 12v maintenance software .... clueless comes to mind ...

T1 Terry

Hi T1 Terry.

I'm not a lead-acid battery specialist, so hope you won't rip-my-head-off if I ask clueless questions or appear to challenge any of your points.

1) it sounds like your comments above relate to traditional, flooded, lead-acid batteries ...pls clarify
2) for an EV, a traditional 12V battery (which is great for short duration, deep discharge operation) is a poor choice.
3) for an EV, AGM batteries have more suitable characteristics.
4) charging & maintained SoC for AGM differ from Trad batteries; AGM should not be fully charged, but perform & have a longer life with PSoC.
5) from what [I think] I understand, the way my S5 is treating its AGM 12V battery is consistent with best practice; e.g. lightly (PSoC) recharging the battery from the traction battery when terminal voltage drops to ≤ 12Volts. Since traction battery has almost 2000 times the capacity of the system 12V battery, the car should remain 'healthy' even if left 'parked up' for several months, assuming the car was initially charged to (say) 80%.

Any comments so far?

I got AI to compile a comparison of traditional flooded 12V (ICE) batteries with ev 12V AGM.

Probably too much to paste, so attached as a pdf.

From the table of typical SoC % for terminal voltage, it looks like my S5 is trying to keep its AGM battery between 30% - 80/85% approx (12.0V to 12.7V).

This is pretty much what I do with my phone: 20 - 85%. ...different battery technology, but for similar reasons.

 

[T1 Terry]

Sorry, this turned into a long post and I did try to only touch on each part ....

I was taught "there is no such thing as a silly question" when I was doing my Cert 4 training and assessment course .... I gotta tell you, I've had some training sessions where participants challenged that idea but this isn't one of them, so you can breathe easy

Maybe an explanation of the types of lead acid batteries might help answer these questions ..... The first one, there are start batteries and there are deep cycle lead acid batteries, some claim to combine the two and call them marine batteries, unfortunately, they combine the worst sides of each type, not the best.
If you want me to explain how to tell them apart and how to desulphate each type, just ask ... I'm happy to bore people with information

I'm guessing by traditional lead acid you mean flooded cell.
These originally had a cap on each cell and the idea was to keep the electrolyte up to the little tangs that can be seen where the cap goes in .... even this fact isn't well known.

The next version of this was the Magic Eye or similar names, where there was a clear plastic removable cap with an indicator under it, I think:
Blue was OK
Red said the specific gravity was low and it needed charging
Clean meant it needed topping up with distilled water

The next version had a see through case so you could see the electrolyte level, but you had to peel the brand label off to find the filler caps

The latest version is "sealed battery" and has a vent tube out the side, when the electrolyte gets low .... there is nothing you can really do about it, possibly try injecting distilled water in the trough the vent tube and then put the end of the vent tube into a plastic drink bottle, you can use that the next time it needs the electrolyte topping up
These are the ones you referred to as best not to fully charged, the manufacture used the line that over charging was the cause on electrolyte loss .... a very handy distortion of the truth, desulphation and cell equalising does involve electrolysis where the water component breaks down into hydrogen and oxygen ..... that frantic bubbling seen in the cells of a removeable cap flooded cell battery when equalisation charging .....

The next upgrade was AGM (Absorbed Glass Mat) where limited electrolyte was used, the fibre glass mat held the electrolyte against the plates and the cells had a thing called a recombiner under where the cap went, and the use a catalyst to recombine the hydrogen and oxygen into pure water and drip it into the electrolyte
This idea works well when a battery is held at 14.4vdc for one type and 14.8vdc for the other type, I believe the higher voltage was for colder climates ..... This recombining unit generates heat, so does equalisation charging, so the 16.5vdc for equalisation was discouraged due to the heat generated by the recombiners adding to the heat generated by electrolysis ......
Unfortunately, this rapid bubbling also helped remix the concentrated acid in the bottom of the cell with the pure water being added in droplets to the top of the electrolyte from the recombiners ..... this unmixed electrolyte is known as stratification ..... the pure water at the top of the cell doesn't have any sulphur in it, so it can't chemically react with the lead, so it can't generate any electrical energy, while the concentrated acid in the lower part eats the lead acid plates away ..... so that bubbling charging voltage level being maintained is important to achieve this electrolyte mixing as well ....

The next brain child was gel cell battery. These hold the electrolyte in a gel format so are spill proof. They don't suffer stratification or electrolyte loss, sounds great, but the catch is, the charge rate and voltages need to be very carefully controlled.
Charged too fast and bubbles form between the gel and the plate, rapid discharge has the same affect. These bubbles are trapped, leaving an area where the gel electrolyte no longer comes in contact with the plates, each bubble is a tiny loss of capacity and therefore, a reduction in the charging absorption rate and discharging capabilities ... without generating more bubbles .... the death cycle .....

The last and latest is lead crystal batteries. These have crystalised electrolyte, they can be deeply discharged, but the capacity recovery regime is a serious procedure, requiring charging and discharging on a repeated cycle until the capacity is returned .... works great in the lab, hopeless in the real world.

T1 Terry