Charging Batteries With Built-In Hydrometer "Eye; More On Electrolyte Stratification - Craftsman 934.716140 Owner's Manual

CHARGING BATTERIES WITH BUILT-IN HYDROMETER "EYE"
CHARGING BATTERIES WITH BUILT-IN
HYDROMETER "EYE"
Often, maintenance free lead-calcium batteries are equipped with
a built-in hydrometer "eye" that indicates the battery's state of
charge (such as the Delco Freedom). Many deep-cycle batteries
are also equipped with this "eye". In order to make the "eye"
indicate properly at full charge, it is important to follow these
instructions.
1. Always charge these batteries with the BATTERY'TYPE
SELECTOR set to DEEP-CYCLE, regardless of battery type.
2. After the green CHARGE COMPLETE indicator comes on, it
may take more than 1 hour for the "eye" to indicate full charge.
.
Always follow the battery manufacturer's instructions. Some
recommend tilting or lightly shaking the battery once an hour
during charging. This helps mix the acid that has stratified
during charging, with the stronger acid at the bottom of the
battery.
NOTE: Regardless of whether or not the "eye" indicates full
charge, if the green CHARGE COMPLETE indicator comes on,
the battery is at full charge.
More On Electrolyte Stratification
When a battery is charged, the electrolyte around the plates in the
battery will increase in specific gravity faster than the electrolyte
above the plates.
The built-in "eye", found in many of today's batteries, is a
hydrometer that measures the specific gravity of the electrolyte
above the battery plates.
When a battery being recharged, finally reaches full charge
(specific gravity of 1.265), the electrolyte above the plates of the
battery will have a specific gravity of only about 1.1 90, or 50% of
charge. But the electrolyte surrounding the battery plates will
have a specific gravity of as much as 1.300, or about 110% of
charge. When these two layers of electrolyte finally mix, the
resulting electrolyte will have a specific gravity of 1.265 or 100% of
charge.
Since the "eye" is reading the electrolyte above the plates, it will
not initially indicate full charge when, in fact, the battery is at full
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