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Battery Data


Lead Acid Batteries

This data is from the Yuasa "Battery Handbook and Technical Guide"
Yuasa-Exide
P.O. Box 14145
Reading, PA 19612-4145


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 ChargeHydrometer reading Unloaded Voltage
1001.24212.49
751.18712.16
501.13711.86
251.09711.62
01.07711.50

Temperature: 17 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.24512.51
751.19012.18
501.14011.88
251.10011.64
01.08011.52

Temperature: 27 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.24812.53
751.19312.20
501.14311.90
251.10311.66
01.08311.54

Temperature: 37 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.25212.55
751.19712.22
501.14711.92
251.10711.68
01.08711.56

Temperature: 47 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.25512.57
751.20012.24
501.15011.94
251.11011.70
01.09011.58

Temperature: 57 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.25812.59
751.20312.26
501.15311.96
251.11311.72
01.09311.60

Temperature: 67 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.26212.61
751.20712.28
501.15711.98
251.11711.74
01.09711.62

Temperature: 77 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.29512.63
751.21012.30
501.16012.00
251.12011.76
01.10011.64

Temperature: 87 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.26812.65
751.21312.32
501.16312.02
251.12311.78
01.10311.66

Temperature: 97 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.27212.67
751.21712.34
501.16712.04
251.12711.80
01.10711.68

Temperature: 107 degrees Fahrenheit

Percent ChargeHydrometer reading Unloaded Voltage
1001.27512.69
751.22012.36
501.17012.06
251.13011.82
01.11011.70


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 ChargeSpecific Gravity Degrees Fahrenheit
1001.265-75
761.225-35
741.200-17
501.1505
01.10018
<01.05027



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.



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