Flooded Lead Acid batteries, popularly called FLA batteries, are the most popular of all the types of lead acid batteries. They have a long proven history of use; they have been in use for hundreds of years.

FLA batteries are so called because they contain an excess of electrolytic fluid so that the +ve and –ve plates are completely submerged. As the batteries discharge, the chemical reaction thattakes place produces oxygen and hydrogen which are released from the batteries. As a result, the level of the electrolytic fluid starts reducing. But it is very important to maintain the electrolytic fluid level above the top part of the plates and never expose them. If that happens, the plates get damaged and their life reduces considerably. The way to do it is to periodically fill them with distilled water. This is the main maintenance activity that has to be performed on FLA batteries.

The main advantages of FLA batteries are:

  • They have a long proven history of use.
  • They have a high discharge rate capability.
  • They perform better in hot climates.
  • They perform much better than Valve Regulated Lead Acid (VRLA) batteries (or maintenance free batteries or SMF batteries as they are popularly called) when regularly in a partial state of discharge (PSoC).
  • They have the lowest price of all the lead acid battery types.

The main disadvantages of FLA batteries are:

  • They need to be periodically refilled with distilled water. This is a major part of the maintenance activity that needs to be performed on FLA batteries and is a major cause of concern if the batteries are installed in remote locations or in areas which are not easy to use, like for example in solar street lights.
  • They have a higher self-discharge rate as compared to VRLA batteries, which means they cannot be stored for long periods of time without charging them periodically to ensure that their state of charge (SoC) doesn’t fall below the 50% level.
  • They can only be used in an upright position.
  • They cannot be installed in places with no ventilation or poor ventilation since they release gases during the normal operation and more so while charging.
  • They cannot be kept in the vicinity of any electrical equipment or any inflammable material.
  • They may emit acid spray if overcharged abusively. Therefore, it is important to properly follow the safety instructions while working with FLA batteries.
  • They cannot be shipped by air; they necessarily have to be shipped by sea.

The main disadvantage of FLA batteries is that they have to be filled with distilled water periodically, which is called “topping up” the batteries. How often it has to be done depends on how good or how bad the batteries are, and can vary from once in a month to once in six months. However, if the batteries are not used properly, i.e. if they are charged or discharged abusively, then you might have to add distilled water once a week or even once a day.

However, this main disadvantage of FLA batteries can be overcome by using automatic filling systems. For a small fraction of the costs of the batteries, these automatic filling systems take care of maintaining the electrolytic fluid levels in the batteries, which goes a long way in ensuring that the batteries for as long as they can, and are therefore worth every penny.