Vented lead acid batteries – or VLA – are unique power sources that require dedicated monitoring and maintenance.

Also known as flooded batteries, VLA batteries are used for backup power applications in the utility and telecommunications industries, data centers, grid energy storage and backup power supplies.  They are also used in motive applications, such as forklifts and submarines.

Let’s compare VLA batteries to Valve Regulated Lead Acid Batteries, or VRLA, to illustrate their differences. VLA batteries are vented and require monitoring of their electrolyte levels, while VRLA batteries require reduced maintenance since they are sealed.

VLA batteries are typically larger, hold a higher charge capacity, have a longer life, cost more and are more resistant to overcharging than VRLAs.  (Additionally, VRLAs may enter a thermal runaway state, which could trigger a catastrophic fire.)

Strict monitoring is essential for VLAs to ensure optimal performance. This type of battery produces hydrogen and oxygen gasses under both normal and abnormal operating conditions, but especially during an overcharging state. The excess charge electrolyzes the electrolyte mix of sulfuric acid and water, causing the hydrogen and oxygen to escape from the battery. VLA battery gassing depletes the water in the battery and distilled water must be added as part of its maintenance. Safety is of the utmost importance and care must be taken to avoid breaking the VLA since it contains sulfuric acid.

In order for the VLA battery to operate at optimal level, its plates must be immersed in the electrolyte, composed of water and sulfuric acid. Once gassing occurs and the plates are exposed, they become inactive, reducing battery capacity, thereby compromising its ability to provide the needed energy during a power outage. How can someone have the confidence of knowing all the flooded batteries have the correct electrolyte level and thus operate at optimal performance?


The solution to VLA battery maintenance and optimal function is an electrolyte battery monitoring system. While there are many products on the market, the Midtronics CELLGUARD SYSTEM-ELS+ Electrolyte Battery Monitoring System has many outstanding features:

  • It is small, can be easily installed and there is no maintenance required.
  • Unique wiring is daisy-chained from one sensor to the next without a return path wire, which makes installation clean and neat.
  • The HUB alarm unit can be placed on either the left or the right side of the physical battery string with daisy chained ELS+ sensors – which adhere to the battery case with a 3M adhesive foam padding. No glue resin necessary.
  • The ELS+ triggers an alarm for low electrolyte levels as well as a temperature readings exceeding set threshold limits and power loss to sensors
  • Can be integrated with common commercially available data collection systems
  • Compatible with VLA batteries of any voltage, size or design that are not opaque

CELLGUARD SYSTEM-ELS+ increases safety by reducing frequency of close contact with batteries and battery acid. It increases reliability of the battery and protects a company’s large investment. The monitoring system saves time and travel and supports NERC PRC-005 compliance.