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How Often do you Equalize your Batteries ?

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Rob Beckers:
Just wanted to add my 2cts, for what it's worth...
I don't live off-grid, but have been in the off-grid business for a very long time now. We used to install systems, many of them off-grid. These days the business limits itself to designing systems and supplying parts. The 'long time' part means I get to see how well, or not, customers manage their batteries.

My observations are that there's no real need to equalize flooded lead-acid batteries on a regular basis. The same is said by the battery reps when I talk to them. Even the ones that do prescribe period equalizing (it's a choice between two evils). Equalizing is hard on batteries, you are (to some extend) trying to shed lead-sulphate by mechanically bubbling the plates, freeing up new lead to participate in the reaction. You're losing some plate material. The advise I give people these days is to track specific gravity and equalize when needed.

If your batteries bounce back regularly (every couple weeks) to an SG of 1.265 - 1.270 then what would equalize do for you? The lead-sulphate is already reverting back to lead and lead-oxide, or you wouldn't reach that SG value. Equalizing isn't going to add anything to that, it's just going to be rough on the plates.

Now, if you see SG values after a full charge declining and inching up the bulk Voltage and absorb time isn't remedying the situation, by all means, equalize! This is often needed after winter (not a lot of sun this far north in winter), in particular when people were reluctant to run their generator due to fuel cost.

The parameters I give people asking when to equalize are when cells drift apart (after a full charge) by more than 0.025, or when cells no longer reach 1.250 - 1.255 (for the common brands, fork-lift batteries run a little 'hotter' at higher SG values). For a 12V system equalize would constitute about 15.8 Volt for 2.5 hours (if you can). After that measure SG and see where things are at. If multiple equalize sessions are needed space them apart by a week or so, let the cells get back into the swing of things before kicking them again. For most people/systems solar alone won't cut it to equalize, not enough oomphf (highly technical term!), and a generator is needed (with a charger, or inverter-charger).

If you find yourself equalizing batteries every couple of months because they need it, have a hard look at things. Something else is wrong. Those that get 15 years out of 12-year design-life batteries consistently have a setup where there's enough solar PV (or other charging sources) that they see a full charge regularly, they're cycled not too deep most of the time (20% - 30%, though there's an argument to be made that you're spending too much on batteries if that's all you do with them), and they have long absorb times. That last part is very misunderstood by many; Even if you you charge batteries at 15% of their Ah-rating (and that's about as high as I would go for flooded lead-acid due to heat), it will require just about 3 hours of absorb time! Most systems can't charge consistently at that rate, and essentially need all day (or as long as the sun shines) to do a proper absorb charge....

-RoB-

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