🔍 Key Concepts

• Lead-acid battery state of charge (SOC) and how it is commonly checked on vessels • Use of a hydrometer to measure electrolyte specific gravity • Relationship between battery voltage, load, and accurate SOC indication

💭 Think About

• Think about which instrument is specifically designed to measure the state of charge of a lead-acid cell by sampling the electrolyte. • Consider what happens to a battery’s voltage when it is placed under a heavy load—does this give a stable, accurate indication of true state of charge or can it be misleading? • Ask yourself whether both listed methods are standard, recommended practices for checking the charge of a lead-acid storage cell, or if one is more of a rough/indirect indication.

✅ Before You Answer

• Verify which method directly measures electrolyte specific gravity, which is strongly tied to state of charge. • Consider whether voltage measurements for SOC are normally taken under load, off load (open-circuit), or after a rest period. • Confirm from your engineering/electrical notes which methods are listed as standard practice for determining lead-acid battery charge on board.