It is also developing indigenous Type-IV class submarine batteries and inter-cell connectors, the first set of which has passed all harbour trials after installation on board. Currently, Exide has the capability to manufacture batteries for Class I, II and III submarines only.

The company is chasing a repeat order of batteries for nuclear submarines from the Indian Navy and is also working on furthering its export.

“A repeat order for two sets of Type-II submarine batteries for the Indian Navy along with an export order for a set of Type-I submarine batteries is also being pursued,” the company’s 2019 annual report stated.

Type-II (ATV) batteries are used in nuclear submarines, while Type-I are used in Kilo-class submarines.

Last fiscal year, Exide exported two sets of new-design submarine batteries along with all accessories and spares to the Vietnam Navy, after obtaining the necessary export permission from the Indian government, in a development that marked its entry into the global U-boat battery market.

Exide said the first set of such batteries has passed sea trials and the second set is due for commissioning soon.

Last year, it had also secured a maiden order to make and export one set of batteries for a mini-submarine, which is expected to be supplied during the current financial year.

Exide is among the very few specialised firms that can make high-end batteries for a wide range of submarines such as the Russian Kilo, 636, Romeo and Foxtrot class, German 209 class, French Scorpene class and indigenous nuclear submarines.

Some of these batteries have a 20,000 Ah capacity. Its batteries used in Russian-origin submarines are also certified by that country's design agency, Rubin Design Bureau, as being compliant with their norms.