What must older apparatus batteries have added to maintain cell fluid levels?

To maintain the proper function and longevity of older apparatus batteries, it is essential to use distilled water to manage cell fluid levels. Distilled water is free from impurities and minerals that could corrode the internal components of the battery. As batteries operate, they can lose water through the process of electrolysis, which strips hydrogen and oxygen from the water in the battery electrolyte solution. Regularly adding distilled water helps ensure that the electrolyte content remains balanced, which is crucial for the battery's performance and safety.

Using other substances like mineral water or battery acid can introduce contaminants or alter the chemical balances within the battery, potentially leading to reduced efficiency or even damage. Cleansing agents are also unsuitable, as they may contain chemicals that could harm the battery's structure or performance. Thus, relying on distilled water is the best practice for maintaining the health of older apparatus batteries.