battery checkup mid-2011

I’ve heard a lot of different things about when to equalize and when to add water. Currently I’m of the thought that equalization is only necessary if the specific gravity of each cell varies by 0.007 g/ml or more from the average and that watering is needed when the electrolyte falls below the “manufacturer specified level” – but never, never, never let the electrolyte fall below the level that exposes the battery plates to air or be prepared to suffer the consequences of capacity robbing chemical processes and shortened battery life.

Aside from checking the specific gravity of each cell I also added between 1200 and 1300 mL of deionized water to 14 batteries or 42 cells; about 30 ml/cell. This is the first watering since the batteries were purchased. At our current pattern of use (120-130 days use/year of 150-350 Ah per day) it seems prudent to measure S.G. and check battery water level twice a year. After all, this our first watering since the battery purchase almost exactly 2 years ago. Our 6V 220 Ah golf cart FLA batteries are labeled as being produced on 8/09.

*chart format updated 11/7/2012

A quick explanation of my chart:

1. Specific gravity is measured and recorded along with battery temperature
2. The spreadsheet then fingers out the measured average S.G.
3. The spreadsheet then figures out the temperature corrected S.G.
4. Below the measured values are the deviation from average of each cell (S.G. and temp)
5. The spreadsheet is also set up to highlight cells that may be getting too far from normal (brown)

And as far the chart goes – I really only care about the deviance from mean of the cells – the rest of the measurements are more or less trivial or simply fun to know. I could probably just stop at measuring the cells and forgoe all of my calculations. Perhaps as the batteries age and slowly lose capacity this will be reflected in my measurements and calculations. At some point, when the battery SOC drops below 70% I’d like to get a S.G. and compare the true battery SOC to the BMV 600s stated SOC. I attempted to compare my 7-31-11 readings this way but I had difficulty because the “full charge” state of batteries appears to vary or flux too much and my reading was taken too close to a full charge (96.3% SOC). For instance, I’ve found charts claiming the 100% charge is anywhere between 1.277 and 1.270 g/ml S.G. and I’ve measured it to a temperature corrected 1.280 g/ml.