The countdown clock has once again started. We’ve begun gearing up for departure, and it’s now time to give Eagle Too a thorough physical. We need to make sure that she’s in tip top shape and ready for the long trip ahead.
One of the first items on the checkup list was to make sure that our batteries are still youthful and fit. We installed them about 18 months ago, which means that in people years they’d be finishing high school and starting their freshman year of college about now.
Back in a post from last year called More Power Scotty, Part Two, we talked about the reasons why we preferred flooded lead acid batteries over other types. One is the ability to take individual cell readings with a hydrometer to monitor their function, something that’s impossible with AGMs or Gel cells. We don’t want any unpleasant “Holy crap, the batteries suddenly won’t take a charge!” incidents while we’re deep down island, days or weeks away from a marine chandlery.
It’s a pretty simple process. While performing this month’s battery level checks and topping off the cells with water, I took a moment to sample the acid in each cell with a hydrometer to measure their specific gravity.
The results tell us two things. First, we were looking for all the cells to be at about the same reading. A cell that’s reading significantly higher or lower than its neighbors is a harbinger of doom. And second, comparing the readings obtained to a specific gravity chart gives a good measure of the state-of-charge, which can be used to validate the reading on our battery monitor.
Here were our results:
Not all exactly equal, but within the normal and expected range. Most of the measured difference could possibly be chalked up to interpretation, as it can be a bit tricky to read the scale on the hydrometer accurately.
Once we had our readings, I then compared them to the data in this handy chart:
Based on our specific gravity measurements, our batteries were at just under 90% state-of-charge. And sure enough, when I checked our battery monitor, it read 88%.
I think we can check this one off as ready to go!