The FAA has approved eight valve-regulated sealed lead acid batteries
under Technical Standard Order C173 for Concorde Battery.
The TSO-approved models are Concorde’s RG-121 Series and RG-122 Series, emergency batteries for lighting, standby, avionics, fadec and backup power. Parts conforming to TSO C173 are approved for design and production.
According to the company, the RG-121 series and RG-122 series are maintenance free and never require replenishment of water or electrolyte. Available with or without internal heaters, all of the batteries are self regulating on charge.