Equalising a dying battery

I have read that you should equalise batteries that have reduced performance (Flooded Lead Acid), which involved charging them at a higher voltage 15.5 - 15.7V and letting them gas and bubble to break up the sulphur deposits (they must be fully charged to perform equalisation). Of course you should check the electrolyte level before hand. This gives up Hydrogen which is flammable so it should be done with good ventilation. I have noticed that most people give the advice to simply replace the battery. Is my perception wrong about equalising batteries? Is this pseudo science? Can the experts please shed some insight? I tried it a month ago on my gate motor “sealed” battery that was failing to open the gate when loadshedding starts, took a stanley knife, popped the cover, added some distilled water and “overcharged” the poor battery for 2 hours. The battery is still opening the gate a month later, but I am not ready to declare it a success, I am still expecting it to fail at any moment. I am pretty convinced that the “pulse” chargers are selling snake oil. To me it makes more sense to push a current through a fully charged battery with a higher voltage, I can measure the voltage and I can hear the cells bubble. Any opinions?

As I understand it the elevated voltage is not about breaking up sulphation, but rather to force current through the battery to ensure that all the cells get a good charge (aka, equalise, as the name implies).

If you don’t do that, and one of the cells is lower than the rest, then the charge current drops off as soon as the other cells are full and that cell may never receive a decent charge.

Of course, forcing current through the battery sacrifices some of the electrolyte. So generally it is only advised for flooded batteries, as you noted, since you can top them off again.

There is another thing to be wary of: In old batteries, there is often a layer of active material lying at the bottom, material that’s been shed from the plates over its lifetime. In really old “glass” batteries they even have a large gap at the bottom precisely so it can safely sit out of the way. Violently charging a battery and mixing that stuff back into the electrolyte is not necessarily a good thing. In other words, for batteries that are really far gone… a hard charge can make things worse.

But with that said, I’ve heard that many people have success – or at least get some extra life out of the batteries – by giving them a nice hard and long absorption charge. So I suppose it is one of those YMMV things.

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You can’t equalize a SLA battery!
These batteries only provide a 5 year (theoretical) life. Typically 3 years if you’re lucky…
If you want to prolong their life only use them when you have to and NEVER leave them in a discharged state!

Why do you say I can’t?
The cover is glued on and it has normal venting caps with a small rubber cover that acts like a one way valve, mechanically it is possible. Chemically it is also possible. So I do not understand your reasoning.

My options were to equalise… or to replace the battery.

My gate keeps the battery under a constant charge, it only works when you open/close the gate. During load shedding it might discharge but as soon as the power is back it charges back up.

Thus far the battery is performing, so I am cautiously optimistic.

Well, you can… but you have limited opportunity. The important thing to remember is that when you do this to a sealed battery, you will cause the venting valve to open and it will make that whistling sound (if the venting valve is blocked, it will blow up like a balloon). While it is doing this, the battery is losing hydrogen and the normal recombination mechanism (that turns it back into water) will not work, so you will lose electrolyte.

The battery can however survive some electrolyte loss, and if you are dealing with a battery that is already half-gone and you’re trying to salvage a few more weeks, you may have nothing to lose and a controlled equalisation may help.

For the most part, however, you are absolutely right. Sealed batteries should not be equalised, definitely not regularly. Balancers can help (but cannot deal with a cell somewhere in the middle of a pack).

Since the topic indicates that we’re dealing here with a dying battery, I’d say it might be worth a shot.

And here’s what Battery University has on the subject:
Equalizing VRLA and other sealed batteries involves guesswork. Observing the differences in cell voltage does not give a conclusive solution and good judgment plays a pivotal role when estimating the frequency and duration of the service. Some manufacturers recommend monthly equalizations for 2–16 hours. Most VRLAs vent at 34kPa (5psi), and repeated venting leads to the depletion of the electrolyte, which can lead to a dry-out condition.

Exactly. It definitely doesn’t say it cannot be done, just that doing it involves guesswork. I also agree that if the battery is already almost dead then it can’t really hurt to try an equalize charge.

Keep us posted…