The True Blue Power division of Wichita-based Mid-Continent Instrument submitted an application for STC approval to install its TB44 lithium-ion main-ship battery in all Cessna Caravan 208s and 208Bs. It expects to receive the STC in the fourth quarter, though it secured FAA and EASA technical standard order approval for the battery in  October.

The Caravan is the first publicly announced application for the TB44. At the time of TSO approval last year, True Blue Power said a number of manufacturers were planning to integrate the 46-amp-hour TB44 and smaller 17 amp-hour TB17 into helicopters, turboprops and business jets. Both are 28-volt units.

At 53 pounds, the TB44 weighs 40 percent less than existing Caravan lead-acid or nicad batteries; delivers up to three times as much energy per kilogram; offers two-year maintenance intervals and 50- to 90-percent lower scheduled maintenance costs; higher voltage for starting and faster recharge after engine starts; and six to 10 years of useful life, according to True Blue Power. 

Both batteries include an internal heater, which ensures full-rated performance throughout their temperature range: -40 (TB44) and -30 (TB17) to 70 degrees C. For operators in remote areas, the TB44 is equipped with a pushbutton to activate the heater in extreme cold. The pilot simply pushes the button, and it takes 30 to 40 minutes to warm up using the battery’s own power, eliminating the need to carry the battery indoors to warm it up.

The underlying chemistry of the TB44 and TB17 is the same that is used in True Blue Power’s standby battery systems: nanophosphate lithium-ion developed by battery manufacturer A123 Systems. The TB44 contains 152 A123 TC3 (ANR26650) battery cells, grouped in bunches of eight to make 19 modules. The TB17 contains a total of 56 TC3 cells. The lithium-ion chemistry in the A123 cells is the iron-phosphate type, not the metal oxide used in the Boeing 787 and automobiles such as Tesla electric cars and Chevrolet’s Volt. The innovation that A123 developed is manufacturing batteries using nanophosphate, tiny phosphate spheres incorporated into the battery’s cathode. The key chemical reaction takes place on the surface of these spheres, and because there are so many spheres, the reactions occur over a much larger surface area. According to True Blue, “The surface area helps the reaction occur faster, allowing for the high-current discharge that is required for engine starts. The increased surface area of the cathode is primarily designed to reduce resistance and increase current/power. It may have some ancillary benefits for cycle life, but that is primarily a function of the iron-phosphate, not necessarily the 'nano.'