Built-In Hydrometer

Maintenance-Free Battery:

Built-in Hydrometer:

The sealed battery has a built - in temperature-compensated hydrometer (also known as "test indicator," "state of charge indicator," or "eye") in the top of the battery. Built-in hydrometers provide a go/no go' indication of the battery state of charge, based on the specific gravity of the electrolyte. Use the hydrometer with the following diagnostic procedure.

Important
^ Ensure that the vehicle is relatively level.
^ When observing the hydrometer, make sure the top of the hydrometer is clean.
^ Use a light in poorly-tit areas.
^ Always tap the hydrometer lightly on the top to dislodge any air bubbles that might give a false indication. Normally, one of three things will be seen:
1. GREEN EYE - If any green can be seen in the hydrometer, the battery is at about a 65 percent state of charge or above and may be tested.
2. BLACK OR DARK EYE - If the green dot cannot be seen and there is a cranking complaint, charge the battery as described under "Battery Charging". Also check the charging system, refer to Charging System.
3. CLEAR OR LIGHT YELLOW EYE - If the hydrometer appears clear or light yellow, the fluid level is below the level of the hydrometer. This can be caused by excessive or prolonged charging, a broken case or excessive tipping, causing electrolyte to leak out through top vents. If this happens, it could mean high charging voltages caused by a faulty charging system. Check the charging system, refer to Charging System.

If a cranking complaint exists and the hydrometer is clear or light yellow, replace the battery. Do not charge or test a battery whose hydrometer is clear or light yellow.

Built-in hydrometers are subject to the following operating characteristics:
1. There is a time delay in having the hydrometer indication change at about a 65 percent state of charge during both charge and discharge. This is due to the slow mixing of electrolyte. The lower the charge or discharge current, the longer the time delay. Therefore, when working with batteries that have been in use, tested or discharged within the last 24 hours, remember that the built-in hydrometer may not be giving a stabilized indication. Check the built-in hydrometer again after 24 hours to be sure the indication has not changed.
2. When recharging a battery that had a dark indicator, the time delay of the green dot's appearance actually helps the technician do a better job because the plates will be around 90 percent charged by the time the green dot appears.
3. When battery power is used during vehicle repair (such as repeated engine starts, lamps and accessories left on, etc.), remember the hydrometer indication is delayed. A green dot indication right after such vehicle repair may not always mean the battery is still adequately charged. To ensure customer satisfaction, charge the battery to replace the power that was used. A 15 to 20 ampere charge for an hour will usually be enough to restore a slightly discharged battery.
4. Use a battery charger that is capable of charging the battery at a level of at least 16 volts. Not only does this help to recharge in a reasonable amount of time, it also promotes mixing of the electrolyte in the battery. This minimizes the delay in the hydrometer indication.
5. Remember that the built-in hydrometer only indicates the condition of one battery cell. In a normally functioning battery, all cells will have nearly equal specific gravity and electrolyte levels. The hydrometer should not be used as the only indication of a fully charged battery.