The service life of many substation batteries was ending: capacity had become too low, rectifiers were damaged, DC wiring was obsolete and telecontrol links were absent. EU Regulation NC ER on system restoration also imposed new requirements. Most substations still had only a single battery section, so temporary batteries had to be installed during replacement. This involved additional risk because each station needs continuous DC supply to remain online for dispatch. The works had to be performed on substations in Retkinia, Janów, Sulejów, Lodowa, Pabianice, Roszkowa Wola, Komuna Paryska, Sieradz, Jawor, Żyrardów and Brzeziny.