Aircraft batteries are notoriously unreliable, but they get an unfair rap. Unlike our reliable car batteries that we generally use daily and keep in a garage out of the worst of the elements, an aircraft battery may sit for weeks or months between uses, and many are exposed to extreme heat and cold. Not to mention that on a normal turbine start, power draw can exceed 1,000 amps or more.
Turboprop models of Twin Commanders use two 24-volt batteries installed in the fuselage, just aft of the baggage compartment. Battery power is used for starting and as an emergency backup to the generators. On early airplanes they are connected to the main bus and the start bus, and on late model airplanes to the tie bus and start bus.
Although most pilots will limit their checks of the battery to voltage verification before starting, FAR Part 43 empowers them to also replace and service the batteries. At a minimum, it’s prudent for the pilot to visually inspect the battery on a semi-regular basis. A quick check to ensure the batteries are securely mounted and the electrolyte isn’t spilling is a good place to start. Electrolyte spillage is seen by inspecting the battery and battery box vent tubes for signs of moisture.
Pam Brown, Twin Commander Aircraft’s operations lead, said that she fields many calls from technicians and operators about the airplane’s batteries. Many ask about the approved part numbers for a simple replacement, but occasionally batteries have been known to cause more significant problems. One had spilled electrolyte years earlier that led to significant corrosion issues that the trays didn’t contain.
In terms of getting the most life from your investment, a little bit of thinking ahead goes a long way toward extending the life of the batteries. The pilot’s operating handbook recommends removing the batteries and keeping them in a cool place if the airplane is going to be stored for longer than 30 days. Nothing is said about charging, although the maintenance manual addresses this. It says to charge the battery anytime the airplane is expected to sit for 30 days, and that they should be removed and stored on the bench if it’s expected to be more than 30 days.
Removing the batteries is an easy process. Ensure the battery switch is off, remove the connectors from the quick disconnect receptacle, remove the vent hoses and cap the vent lines, and pull out the batteries.
With the batteries out, they and the rack can be cleaned with a baking soda solution. Rinse with clean water and dry. A stiff bristle, nonmetallic brush can be used to remove more stubborn material, and the terminals can be cleaned with a wire brush or emery cloth.
The maintenance manual has detailed specifications and instructions for testing and charging the batteries, and for filling the electrolyte. Fully charged batteries have a specific gravity of between 1.275 and 1.295 for each cell, corrected to 80 degrees. Anything lower and it’s time to charge.
Charging shouldn’t exceed 6 amps until the electrolyte begins to bubble, at which point the rate should be cut to 3 amps until four consecutive hourly readings show no rise in specific gravity.
The electrolyte level should be maintained between the bottom of the split ring indicator and the top of the separators, or about 1/8-inch below the split ring. Any higher and the fluid can spill, which no one wants.
If it’s time to replace a battery, you can turn to either Gill or Concorde. Ask Gill for replacement part 7638-44, and Concorde for part RG-380E/44. Both companies have additional information on their websites about battery maintenance and care to make sure the pilot won’t need to call for that GPU cart anytime soon.
