State-of-Charge Test
| Open Circuit Battery Voltage | Approximate State Of Charge | Average Cell SG |
|---|---|---|
| 12.65 + | 100% | 1.265 + |
| 12.45 | 75% | 1.225 |
| 12.24 | 50% | 1.190 |
| 12.06 | 25% | 1.155 |
| 11.89 | 0% | 1.120 |
Use the table to determine the battery's State-of-Charge.
Pay special attention if the DVOM measurement of OCV is equal to:
- 0 volts - Indicate an open cell.
- 10.45-10.65 volts - Indicates a shorted cell.
For non-sealed batteries, check both specific gravity (SG) in each cell with a temperature compensated hydrometer and battery OCV, without the engine running.
For sealed batteries, measuring the battery's OCV (without the engine running) with an accurate DVOM is the only way to determine the state-of-charge.
Batteries with a built-in hydrometer measure the state-of-charge in one cell only. If the indicator is clear or light yellow, the battery has a low electrolyte level and should be refilled before proceeding or replaced.
A state-of-charge reading BELOW 75% using SG, voltage measurement or dark indicator in batteries with built-in hydrometers, indicates the battery must be recharged before proceeding.
Replace the battery if one or more the following conditions are met:
- More than 0.050 difference in the specific gravity readings between the highest and lowest cell (There is a weak or dead cell).
- The battery will not recharge to 75% or greater state-of-charge or the built in hydrometer does not indicate good (green indicates 65% or better).
- DVOM reading indicates 0 volts (Open cell).
- DVOM reading indicates 10.45-10.65 volts (Shorted cell).