## Battery Data

This data is from the Yuasa "Battery Handbook and Technical Guide"
Yuasa-Exide
P.O. Box 14145

Voltage vs percent charge

The Yuasa book has a chart of specific gravity vs. % charge at 77 degrees Fahrenheit. Then they specify that to find the cell voltage (this is the voltage of a single cell, not the entire battery!), one should add .84 to the specific gravity. To find the voltage for a 6 cell (nominal 12V) battery, multiply by 6. It is stated that the specific gravity changes by .001 for every 3 degrees Fahrenheit. I used this data to build these charts from the one supplied for 77 degrees. Since the calculated values for the voltage were off by a small amount at 77 degrees, I used the calculated values in my chart so that it could be compared to the charts calculated for other temperatures.

Note that the voltages calculated are for an unloaded battery. This means that you shouldn't be charging while you take these readings either! I'd suggest waiting 3 hours after disconnecting a load or charger before measuring the voltage.

It is also mentioned that Yuasa's "Sulphate Stop" will make for both higher specific gravity readings and voltages. One presumes that other anti-sulphation products may have similar results.

Temperature: 7 degrees Fahrenheit
 Percent Charge Hydrometer reading Unloaded Voltage 100 1.242 12.49 75 1.187 12.16 50 1.137 11.86 25 1.097 11.62 0 1.077 11.50

Temperature: 17 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.245 12.51 75 1.190 12.18 50 1.140 11.88 25 1.100 11.64 0 1.080 11.52

Temperature: 27 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.248 12.53 75 1.193 12.20 50 1.143 11.90 25 1.103 11.66 0 1.083 11.54

Temperature: 37 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.252 12.55 75 1.197 12.22 50 1.147 11.92 25 1.107 11.68 0 1.087 11.56

Temperature: 47 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.255 12.57 75 1.200 12.24 50 1.150 11.94 25 1.110 11.70 0 1.090 11.58

Temperature: 57 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.258 12.59 75 1.203 12.26 50 1.153 11.96 25 1.113 11.72 0 1.093 11.60

Temperature: 67 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.262 12.61 75 1.207 12.28 50 1.157 11.98 25 1.117 11.74 0 1.097 11.62

Temperature: 77 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.295 12.63 75 1.210 12.30 50 1.160 12.00 25 1.120 11.76 0 1.100 11.64

Temperature: 87 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.268 12.65 75 1.213 12.32 50 1.163 12.02 25 1.123 11.78 0 1.103 11.66

Temperature: 97 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.272 12.67 75 1.217 12.34 50 1.167 12.04 25 1.127 11.80 0 1.107 11.68

Temperature: 107 degrees Fahrenheit

 Percent Charge Hydrometer reading Unloaded Voltage 100 1.275 12.69 75 1.220 12.36 50 1.170 12.06 25 1.130 11.82 0 1.110 11.70

Freezing points vs specific gravity

The specific gravity in this chart is measured at 77 degrees Fahrenheit, at the point where the electrolyte actually freezes, it will be lower.
I'm presuming the last entry (way less than 0% charge) is a battery that's been sitting a long time.
The book didn't have % charge, I was curious and interpolated these numbers from the 77 degree chart above. The reason that 1.15 come out to 50% instead of a lower number is rounding.

Freezing,

 Percent Charge Specific Gravity Degrees Fahrenheit 100 1.265 -75 76 1.225 -35 74 1.200 -17 50 1.150 5 0 1.100 18 <0 1.050 27

Self discharge

According to the Yuasa book, conventional lead-acid batteries discharge at a rate of 1% per day at 77 degrees Fahrenheit. That means that in a bit more than three months, your battery is dead. Faster if your bike/car draws some current when not running, which many modern vehicles do. An increase of 18 degrees doubles the discharge rate. Although not stated, I presume that a decrease of 18 degrees halves it.