Recovering a sealed lead acid battery

[ScottBouch]

Hi all,

We have a 12V sealed lead acid battery that we use 2 or 3 times a year for camping. It's part of a solar PV system on the tent.

Last weekend, it's terminal voltage was down at about 7 or 8 V, so the PV charger unit went into shutdown mode and wouldn't even try charging it.

I then used jump leads from the car to give it just enough terminal voltage for the charger unit to then start giving it a charge from the panels.... It's the first time I've jump-started a tent!

But alas, after several hours of charging, when the sun went down, it wasn't very well charged, and couldn't even run the LED lights or charge a mobile phone over night. In the past, this was a small fry task for it.

I'm assuming that I have killed it through lack of use over it's life. It's about 10 years old, and as said has had months of inactivity between short spells of use for a long weekend, or a week camping, and has now given up.

Before I buy a new battery, I've heard in the past about crystals forming on plates, and a good blast of a higher voltage with a few amps behind it can clear them out, but thinking of potential heat generated, how safe is this on a sealed battery?

Cheers, Scott.

[G6Tanuki]

If it's ten years old then even if it had been meticulously cared-for I would consider it now well past its expected service life.

Spending time and effort trying to resurrect it is unlikely to be a good investment.

WEEE it and get a new one.

[emeritus]

According to the manufacturers' data sheets for SLA batteries that are downloadable from the websites of CPC, RS etc, the standard SLA batteries typically have a specified life of around 5 years, although the traction quality ones we use on our electric bikes are usually good for at least 7 in practice, but they are used for short trips on almost a daily basis, are seldom subjected to deep discharge, and are always put on charge after use. The last lot I got were higher specification ones with a stated 9 year life, but they were twice as expensive.

[The Philpott]

I don't think i've ever had one last beyond 6 years, despite mollycoddling them.
I would WEEE it.
Dave

[ScottBouch]

Ah, brilliant, so we've actually done rather well with tis one then!

Thanks guys, I'll buy a replacement, and probably a bigger one as I've now converted our 3-way camping fridge to Peltier heap pumps (I added variable control to them), and recently added a couple of solar PV panels; ie, it would be good to have enough battery capacity to operate the fridge over night on a low power setting.

Many thanks, Scott.

[G3PIJpeter]

Pry (snap) off the plastic vent caps; remove the rubber cell caps underneath; add distilled water to the top of the plates; carry out several charge / discharge cycles (checking electrolyte levels). Works for most of the dead / comatose 12-volt Yuasa gel batteries that find their way here.

Peter

N.B. Wear eye protection, do not sniff charging cells, do not drink the . . . . etc. etc.

[dougietamson]

Now's your time to go LiFePO4, half the weight and double the amp hours.

[G6Tanuki]

Originally Posted by dougietamson

Now's your time to go LiFePO4, half the weight and double the amp hours.

Agreed! I now use LiFePO4 batteries for my portable SOTA setup and certainly won't ever be going back to lead-acids, or NiMH.

[Andrew2]

I've has success with gel cells that were completely dead by judicious use of reverse charging for very short periods until you see the current climbing. Then charge as normal. I've resurrected a few like this and although they are a bit lacking in stamina now they are still working.

[ScottBouch]

Thanks guys... I'm interested in learning more about LiFePO4 technology... but of course as with all things "consumer" on the internet, there is a ton of conflicting guidance out there, so I again come to ask you guys for some sense!

I have at present a small 12 V MPPT solar PV charge controller. It's designed for lead acid charging. It cuts off charging at a max terminal voltage, and also has a minimum cut-off for battery discharge limit.

The charge controller datasheet: https://www.inverter.com/doc/ATO-PWM-solar-charge-controller-user-manual.pdf

Similar info: http://www.engineer-solar.com/products/products_152.html

As charging rate/profile is uncontrolled in a solar PV system, and purely dependant on the movement of clouds over the sun during a day, could I just use this same charge controller on a LiFePO4 battery? ...or would I also need to upgrade the charge controller too?

Cheers, Scott

[ex seismic]

Like others here I have given up on SLABs and gone to LiFePo4. Have a look at EcoWorthy. I have charged mine from a 14.2v controlled charger originally designed for Slabs.

gmb

[MotorBikeLes]

If you get a lithium battery with three cells, and a charge/discharge circuit, then your existing control, sitting before the lithium pack should be OK. But you MUST have a 3s control fitted. Easy to buy on Ebay. Three cells will have a maximum voltage of 3 Xs 4.2v (=12.6v) quickly falling to 3 Xs 3.7v (11.1v) for most of its operating time.
Les.

[GMB]

First, does your PV charging system do proper lead-acid charging or do you just connect a solar cell to the battery relying on a built-in diode?

Unlike the above reports, I have sealed lead-acid batteries that were bought second hand 13 years ago and they are still working albeit down to maybe 50% of rated charge.

Lead-acid are often "rated" for 5 years service but understand what that means: it does not mean it drops dead after 5 years, it just means it will be out-of-specification so do not expect the Ah rating to be achieved.

The other big issue is that lead-acid must be charged at regular intervals. If you float charge them continuously then the charger needs to be super accurate and temperature compensated. I change all mine using an "intelligent" lead-acid charger every month or two.

Sudden loss of voltage I suspect is about cell balance in batteries. The cells state-of-charge gradually drift apart. With sealed batteries you will loose electrolyte trying to correct this by over-charging. Wet ones can last longer because you can charge them hard and then top the water up.

You can get Li-ion batteries that "look like" common lead-acid types so may cope with crude charging as the real charging is done by the built-in management chips. Li Ion does have the advantage that they like to sit about not bing used but I find it harder to know what their state-of-charge really is (rather than what chargers report).

[cmjones01]

I'm seconding the LiFePO4 route. Lead-acid batteries just aren't worth the bother these days unless you're going for the absolute lowest cost.

A set of four LiFePO4 cells connected in series can be treated pretty much like a 12V lead-acid battery, and indeed they're obtainable in a "car battery" like size and shape if you want. Though the cell chemistry is remarkably tolerant of abuse and vanishingly unlikely to do anything bad, it's very much advisable to have a battery management system (BMS) connected to the cells to guard against over-charging and over-discharging and to keep the cells balanced so that some don't over-charge before others. Suitable ones are available for a few pounds from eBay, Allegro, Aliexpress and so on and seem to work well enough.

I have a small four-cell battery pack of "A123" branded (no longer made, but excellent quality and still available if you look hard) 2.3Ah LiFePO4 cells which I use when we're on family camping holidays. It does duty charging the children's remote-controlled models, charging phones, and powering a pump for inflatable mattresses and unicorns. I haven't got round to fitting it with a BMS yet because I know the cells are closely balanced and I periodically keep an eye on the cell voltages. But I know I ought to. I do use a proper LiFePO4 charger, a simple plug-top one, which wasn't expensive, again bought from a marketplace site.

Chris

[GMB]

I view Li-ion batteries a bit like nuclear power. They are great when they work properly but the consequences of a bad failure are absolutely terrible.

Lead-acid batteries do not combust like a firework, even in a total failure situation - so they are not all bad!

I do not trust Li-ion unless it has a charge management system that was designed for the exact cell type used - and by a reputable manufacturer (or someone who has a reputation to protect so checks their Chinese imports carefully).

What worries me about the cheapo Chinese battery management devices is how would one know that they were done right? Given some other Chinese bits of electronics I have seen where I can tell exactly how well they work (e.g. digitial voltmeter modules) I would say that calibration was a big problem. Battery management devices for any battery type need to be super accurate or they risk a short battery life (best case) or for Li-ion an unscheduled fireworks display.

All batteries have annoying problems. Lead-acid cannot be left alone in a discharged state, while Li-ion do not really want to be charged to 100%. And none of them want to be discharged to near 0%. I think we are still waiting for the "perfect" battery.

[cmjones01]

Don't tar all Lithium batteries with the same brush. LiFePO4 batteries are a very different species from the ones we carry in phones and laptops. They're much more docile chemically and, crucially, don't suffer from thermal runaway.

I've been working with them for years and years, in all sizes from small laptop-battery-sized ones to battery packs that can only be moved by fork lift. I've put them through all manner of abuse, and so have the customers of the products I've designed using them. In that time I've personally seen precisely two cells fail "badly". One I've still got. It's a 100Ah cell and the plastic casing is puffed up. It's been sitting in a box in my storage unit for several years waiting for me to find time to figure out what's wrong with it. Another was in a 4-cell 'car battery' type unit, nominally 12V at about 40Ah. It developed a fault internally while a colleague was working with it, and started to get hot. I carried it out from the office into the car park just in case and left it there for a few minutes to cool off, which it did. No drama.

I wouldn't say the same about the Li-polymer pouch cells that are everywhere in consumer products and children's toys these days. They're definitely a liability.

Chris

[ScottBouch]

Originally Posted by cmjones01

I've put them through all manner of abuse, and so have the customers of the products I've designed using them.

Hi Chris... So in my camping solar PV setup, if I was to just simply replace my sealed lead acid battery with an equivalent nominal 12V LiFePo4, using the same MPPT solar charge controller, do you think it may just work ok?

The MPPT charge controller datasheet: https://www.inverter.com/doc/ATO-PWM-solar-charge-controller-user-manual.pdf

( GMB asked if I was using a charge controller or simple diode in Post 13 https://www.vintage-radio.net/forum/showpost.php?p=1711030&postcount=13 , and yes, I use an MPPT charge controller, see post 10: https://www.vintage-radio.net/forum/showpost.php?p=1710952&postcount=10 )

Cheers, Scott.

[cmjones01]

Yes, it might just work OK. The 'fully charged' voltage of a 4 cell LiFePo4 pack is 14.4V. It looks like that charge controller will charge to that voltage, which is good because that means the cells will be fully charged and you're less likely to run into cell balancing problems. If the charger 'floats' (constant-voltage charges) at a lower voltage, you may find that the cell states of charge become unbalanced because small differences in cell voltage can represent very large differences in state of charge, so constant-voltage charging cells in series at too low a voltage can have odd effects.

It would be advisable to add a BMS module which will cut off the charger if any of the cell voltages go too high, and will balance charge between the cells, but you'll get away without it while the cells are fairly new. It would be hypocritical of me to say otherwise because my battery pack doesn't have a BMS, but battery safety is your responsibility and I would advise checking the cell voltages manually for the first few charge cycles so you can see that everything is OK.

From memory, a LiFePO4 cell is considered fully discharged at about 3.0V (some go down to 2.8V) and fully charged at 3.6V. Over-charging cutout is usually set at 3.8V. For most of the discharge, the cell voltage will sit stably at 3.2-3.3V. It's very hard to infer the state of charge from the cell voltage except at the very start and end of charge/discharge.

Chris

[cmjones01]

Whilst working on something else, I've just discovered that apparently the very popular DeWalt Lithium power tool batteries don't actually do any charge balancing during charging, though the batteries do have connections for it, the charger doesn't use them. They do however monitor individual cell voltages to shut off the battery charger if any one of them goes too high. So even the 'big boys' don't necessarily use a proper BMS.

Chris

[GMB]

On cost I have found that there isn't much difference between Lead and Li.
The cheapness of lead-acid is usually about pro-rata the difference in life, so I am still waiting for Li batteries to become genuinely cheaper.

And I continue to worry about chargers that say they charge "Li" without going into the detail of the many different types. Your charger talks of a wide temperature range, but it must be referring to itself as Li-ion batteries are difficult to charge below freezing point.