Lead-acid battery state of charge — specific gravity at 50% charge When a typical automotive lead-acid battery is about 50% charged, the electrolyte specific gravity at 27°C is approximately:

Introduction / Context:
Hydrometers are used to estimate the state of charge of flooded lead-acid batteries by measuring electrolyte specific gravity. Understanding typical values helps diagnose charging systems and battery health.

Given Data / Assumptions:

• Reference temperature near 27°C (or appropriate correction applied).
• Fully charged battery electrolyte around 1.26 to 1.28.
• Fully discharged battery electrolyte around 1.12.

Concept / Approach:
Specific gravity correlates with sulfuric acid concentration. As the battery discharges, sulfuric acid is consumed and water content increases, lowering specific gravity. Mid-charge (about 50%) falls between the extremes, close to 1.19 to 1.20 for automotive cells at standard temperature.

Step-by-Step Solution:
Recall typical SG values: full ≈ 1.26 to 1.28; empty ≈ 1.12.Estimate midpoint by trend and empirical charts: ≈ 1.19–1.20.Select the nearest provided option: 1.19.

Verification / Alternative check:
Battery manufacturer charts list SG versus state of charge; corrections of about 0.0007 per °C from 27°C may apply, but the nominal midpoint remains about 1.19.

Why Other Options Are Wrong:
0.74 is unrealistic for aqueous electrolytes; 1.00 corresponds roughly to pure water; 1.12 indicates near full discharge.

Common Pitfalls:
Ignoring temperature correction; mixing sealed maintenance-free indicators with hydrometer readings; assuming all chemistries share identical values (AGM/gel may vary slightly).

Final Answer:
1.19