Flooded Lead Acid Batteries
Engineered with T2™ Technology, Trojan Flooded Lead Acid Batteries deliver rugged durability and reliable performance at an affordable price.
Quick Watering Guide for Flooded Lead-Acid Batteries
Why battery watering matters
Flooded batteries require regular watering to maintain performance and lifespan. In this quick watering guide for flooded lead acid batteries, you'll learn best practices for optimal battery performance and longevity.
The best time to water your batteries is always at the end of the charge cycle; however, if the plates are exposed to air, add just enough water to cover the plates before starting the charge cycle. When the charging process is complete, re-check the electrolyte and top off as needed.
Key watering rules
Always water after a full charge. Before charging, ensure plates are covered with water. If discharged, the water level should still be above the plates.
Normal water loss. Water loss during charging is normal due to gassing, which helps mix the electrolyte and complete the charge. However, this also reduces water levels—only add water after charging.
Watering Frequency
Check monthly after installation to establish a routine.
Use distilled water (or de-ionized if necessary, though distilled is preferred).
New batteries may have low electrolyte levels—charge first, then top off if needed.
Proper Electrolyte Level
After charging, water should be 1/8 inch below the bottom of the vent well.
Never let the electrolyte drop below the top of the plates.
Step-by-Step Watering
Open vent caps and inspect fill wells.
If plates are exposed, add just enough distilled water to cover them.
Charge the battery fully.
Recheck levels and top off to 1/8″ below the vent well.
Clean and secure vent caps.
Important Reminders
Never expose plates to air—this causes corrosion.
Never overfill—it can lead to acid overflow and damage.
Never add acid—only water.
Avoid mineral-rich water—use distilled or de-ionized only.
Electrolyte is acidic—avoid skin contact.
Common Mistakes
Under-watering: Can expose plates and cause permanent damage.
Over-watering: Dilutes electrolyte and may cause overflow if done before charging.
Frequently Asked Questions about Watering Flooded Batteries
Water is lost when flooded batteries are charged. The best time to water your batteries is always at the end of the charge cycle. However, if the plates are exposed to air, add just enough water to cover the plates before starting the charge cycle. When the charging process is complete, re-check the electrolyte and top off as needed.
It is best to check your new batteries regularly as this will give you a good sense of how often your application will require battery watering. WARNING: A brand new battery may have a low electrolyte level. Charge the battery first and then add water if needed. Adding water to a battery before charging may result in overflow of the electrolyte.
Yes, de-ionized water can be used instead of distilled water. However, distilled water is preferred because although de-ionized water has all free ions removed, it may still contain some minerals that may be harmful to the battery. In addition, distilled water is generally more available than de-ionized water.
Liquid levels should be 1/8 inch below the bottom of the vent well (the plastic tube that extends into the battery). The electrolyte level should not drop below the top of the plates.
The only way a battery can freeze is if it is left in a state of partial or complete discharge. As the state of charge in a battery decreases, the electrolyte becomes more like water and the freezing temperature increases. The freezing temperature of the electrolyte in a fully charged battery is -92ºF (-69ºC). At a 40% state of charge, electrolyte will freeze if the temperature reaches approximately 16ºF (-9ºC).
It is completely normal for flooded batteries to lose water. They lose water because of the gassing that they go through with every charge. Gassing is an important part of the recharge process. Gassing allows the electrolyte to mix well and helps the battery get back to a fully charged state at the end of the charge process.
Gassing also causes water to be lost. Water should only be added once batteries are fully charged as the electrolyte levels vary as a function of state of charge and are highest once the batteries are fully charged.