Not every battery application offers easy access to recharging. In those situations, engineers are increasingly reaching for a chemistry known as lithium-thionyl chloride.
Lithium-thionyl chloride batteries, which offer some of the highest energy density figures now available, are being employed in military, aerospace, RFID (radio frequency identification), and GPS tracking applications.
A case in point: Vemco, a manufacturer of underwater acoustic telemetry systems, uses lithium-thionyl chloride for long-term underwater deployments where batteries can't be recharged. Vemco employs a battery pack from Tadiran Batteries that combines 24 D-sized primary cells and 12 Hybrid Layer Capacitors in an acoustic receiver.
The receiver is used for remote monitoring of aquatic species tagged with transmitters. During operation, the system's acoustic modem wakes up the telemetry system, transfers data, then returns to a standby mode to minimize power consumption. It enables users to track the migratory patterns of aquatic animals, and to develop early warning systems when sharks and other predatory fish approach beaches.
The battery packs, known as Pulses Plus, enable the system to operate for more than nine years at depths of up to 500 feet.
For a related deep-dive into high-energy rechargables, see our feature-length article, New Breed of Lithium Batteries.