Battery state-of-charge indicator What is the typical specific gravity (at 25°C) of the electrolyte in a fully charged automotive lead–acid battery?

Introduction / Context:
Specific gravity of the electrolyte (sulphuric acid solution) is a quick indicator of the state of charge in conventional serviceable lead–acid batteries.

Given Data / Assumptions:

• Temperature near 25°C (hydrometer readings are temperature-dependent).
• Battery in good condition without stratification.

Concept / Approach:
As a lead–acid battery charges, sulphuric acid concentration increases, raising specific gravity. A fully charged battery typically reads about 1.26–1.28. Discharged batteries approach 1.12–1.18 depending on design.

Step-by-Step Solution:

Verification / Alternative check:
Service manuals and hydrometer charts show green/good zone around 1.26–1.28 at 25°C.

Why Other Options Are Wrong:

• 1.00: distilled water; fully discharged is much higher than this.
• 1.82 or 2.81: far too high; such acid strength is unsafe and not used in batteries.
• 1.10: indicates deep discharge or defective cell.

Common Pitfalls:
Ignoring temperature correction; cold temperatures lower readings, and hydrometers may require adjustment.

Final Answer: