EFB (Enhanced Flooded Battery)
A reinforced lead-acid battery designed for basic Start-Stop. About twice the cycle life of an SLI, at a lower price than AGM.
EFB (Enhanced Flooded Battery) is a reinforced version of the conventional lead-acid battery, with thicker plates, polyester separators and electrolyte additives that improve cycling resistance. It sits between the classic SLI and AGM: roughly double the starting cycles of a conventional SLI, at a lower price than an equivalent AGM. It is compatible with basic Start-Stop (vehicles without regenerative braking, such as many mid-2010s European compacts) but cannot handle the extreme microcycles of advanced Start-Stop, where AGM is required. Typical models: Varta F22 (80 Ah EFB), Bosch S4 E10, Exide EL800.
If your car came from the factory with EFB you can usually upgrade to a compatible AGM, but check first whether the vehicle's management system needs a reset; a conventional SLI must never be installed in place of an EFB original.