Battery Configurations – How About Those Vent Tubes!

The Questions:

The Concorde team spends a lot of time providing battery maintenance training to aircraft maintenance technicians.  During the course of the training seminars, we receive some very interesting questions from attendees.  One of the more popular questions concerns vent tubes.  They range from, “why do sealed batteries have them” and “do I really need to attach anything to them?” to “do they make good handles?” 

The Answer:

In flooded or open cell batteries the vent valves allow hydrogen gas to escape when the battery is charging.     

In a sealed battery, the AGM separator allows oxygen gas generated from the positive plates to diffuse through its pores to the negative plates and recombine with electrons to form water. This recombination cycle minimizes outgassing from the batteries so that the electrolyte never needs to be replenished or topped up.  This also suppresses the evolution of hydrogen gas.  The end result, because the rate of hydrogen emission is very low, only minimal airflow is needed to dilute the hydrogen to safe levels. Most aircraft battery compartments have sufficient natural airflow so a separate air ventilation system is unnecessary.

Now, let’s circle back to the original question; why do you have a sealed battery with vent tubes?  For installation eligibility vent tubes allow for fit, form function interchangeability with flooded batteries.  When converting from flooded to sealed, if the STC does not require removal of the vent lines, the vent tubes provide a place to secure vent lines so they are not flopping around in the avionics bay or engine compartment. When the natural airflow is not sufficient, RG Series batteries are available with vent tubes for connection to air ventilation systems.

Concorde recommends using battery handles where provided. Picking up the battery by the vent tubes can result in damage to the vent tubes or vent tube breakage!