Non-electrified

GTR [Govia Thameslink Railway] currently uses the '171s' on the non-electrified Marshlink and Uckfield lines, and the release of these sets to EMR is contingent on their replacement with converted Electrostar EMUs with bi-mode battery capability, removing these diesel islands of operation from the otherwise all-electric GTR fleet.

The trains are also fitted with small batteries to enable them to shunt at non-electrified depots. Merseyrail is investigating using larger batteries to enable the '777s' to run on non-electrified parts of the system, as it seeks to possibly expand its network.