We toasted our batteries yesterday. Literally. I put our four-stage battery charger in “equalize” mode and pushed the button. For the next four hours, our 12 volt batteries were fried with excess voltage like a condemned murderer sent to the electric chair, until the battery acid actually boiled. Why on earth did we do that? Because it’s good for them. To a flooded lead-acid battery, it’s like a rejuvenating day at the spa.
Now the truth is, the batteries probably didn’t need equalizing. Since we’re mostly tied to the pier and running the battery charger from shore power, the batteries usually stay at a 100% state of charge. It’s when you’re actually out cruising and often don’t have the ability to fully charge the bank that it’s really necessary. When relying on wind, solar, or your engine to charge the batteries, they typically only get up to about 85% or 90% state of charge, and then the acceptance rate slows way down and they only take a trickle of additional juice. So you get tired of running the engine or the generator for hours on end to try and get that last 10–15%, or the sun starts to set on your solar panels, and charging stops. Then that part of your battery that didn’t get charged starts to build up a hard sulphate layer, reducing the battery’s capacity. The purpose of equalizing is to give the batteries a controlled overcharge to convert that lead sulphate (the bad stuff that just takes up space in your battery) back into lead oxide (the good stuff that actually holds a charge).
For the more technically minded among you, here’s what’s going on. This is something I used to have to be able to recite in my sleep back in my submarine days, where as you can imagine, proper care and feeding of the ship’s batteries is a pretty important thing.
Do you need to know this in order to go cruising? Not really. It’s more important that you just have a general understanding of what’s going on and why.
So it’s a new month, and it’s once again time to check the fluid level in our batteries. As I had mentioned in the post More Power Scotty! Part Two, flooded lead acid batteries are by far the best bang for the buck for powering your cruising boat, provided you have the discipline to maintain the fluid levels! We check ours the first week of every month (and spray the terminals with anti-corrosion spray). They were starting to look a little low last month, so I expected them to need some topping off this time. Since it’s normal to have to add some water after equalizing, I thought I’d go ahead and do it before topping off the cells.
But why run an equalization if they didn’t need it? Well, these batteries have been on board now for about five or six months, and I’d noticed that after returning from an afternoon sail or a night at anchor and plugging back into shore power, they were taking noticeably longer to get back to a 100% state of charge. They’d make it to 99.6% or so and then just sit there for a day before they’d finally reach 100%. Now I realize this doesn’t sound like much, I mean, what’s .4% of a 645 amp bank after all? (umm, about two and a half amps). But it looks like it’s going to be another six months or so before we can finally throw off the dock lines and head out, and I want to make sure that when that day comes, our batteries are completely healthy.
Besides, it’s a button that I haven’t pushed in a while (just once when we first installed the batteries) and, well, if you know anything about me, you know how hard it is for me to keep my hands off buttons and knobs and things. 🙂
Robert – I read your series “more power scotty” .. unless I missed something, I did not pick up on the type of charger / inverter that you installed. I think the last writing (part 3) was where you were wiring up the new battery banks but did not tell us the rest of the configuration. I am curious. – Matt
I started writing More Power Scotty! Part Four, in which I’ll go into more detail about the chargers we’re using, but I have yet to take the time to finish the post. In order for it to make sense, I have to create some diagrams that show the old and new charging configuration, and I just haven’t taken the time to create the drawings. Soon. There will also be a Part Five, in which I’ll talk about what we use to monitor the whole electrical setup. And I’m sure there will also eventually be a Part Six, because we’re about to pull the trigger on 500 watts of solar panels. Stay tuned!