Question 41 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is D **Explanation of why option D is correct:** When a lead-acid battery's electrolyte is frozen, it indicates a deep discharge (as fully charged electrolyte has a much lower freezing point than water). Attempting to use or charge a frozen battery is highly dangerous and damaging. 1. **Allowing the battery to thaw naturally:** This is the safest method. Thawing allows the solid ice (which is essentially pure water, since sulfuric acid freezes at a much lower temperature) to melt and remix with the acid concentrate, restoring the liquid electrolyte consistency. 2. **Recharging after thawing:** Once the battery is thawed and the electrolyte is liquid, it must be recharged. The freezing itself is often a symptom of the battery being severely discharged, and a discharged battery cannot provide the high current needed for starting. Recharging restores the chemical potential needed to crank the engine. **Explanation of why the other options are incorrect:** * **A) The engine should be started by means of jumper cables connected to another battery without any particular concern regarding the electrolyte being frozen.** This is incorrect and unsafe. While jumper cables might successfully start the engine, a frozen battery is structurally compromised. The expansion of ice can crack the battery case, damage the plates, and potentially cause an immediate leak of acid once thawed. More importantly, attempting to draw high current (even from an external source) or attempting to charge a frozen battery (which can happen when the alternator starts running) can cause extreme internal pressure, potentially leading to an explosion. * **B) The battery electrolyte should be allowed to thaw, and then the battery electrolyte should be diluted with distilled water as necessary before attempting to start the engine.** This is incorrect maintenance practice. Adding distilled water is only necessary to top off the level if it has dropped due to evaporation or gassing during charging, but it should never be added to dilute the acid strength itself, especially not immediately after thawing. A severely discharged battery needs to be recharged to increase the acid concentration (Specific Gravity), not diluted. * **C) The battery electrolyte should be thawed by means of a battery charger, and then the battery should be recharged as necessary before attempting to start the engine.** This is extremely dangerous. Applying current (charging) to a frozen battery generates heat internally, rapidly converting the ice into steam and gasses. Because the frozen electrolyte acts as a barrier, the pressure builds up rapidly within the battery cells, almost certainly leading to a rupture or explosion. Batteries must never be charged while frozen.