All you need to know about Israelian Submarines:

(To long to post all but worth reading)

[link to www.nti.org]

Extract:
While HDW has stated that Israel's Dolphin-class submarines were equipped with weapon systems similar to those installed on other diesel-electric submarines,[4] various sources have reported that upon their arrival in Israel, the submarines were modified, and fitted with cruise missiles armed with nuclear warheads.[5]

...

The modernized Dolphin-class combines a conventional diesel led-acid battery system and an air-independent propulsion system (AIP) which makes the vessel extremely quiet and allows it to remain submerged for up to a week without surfacing.


..and same page, from the data sheet:
The two most recent submarines that Israel has purchased are modernized versions of the Dolphin-class that include an AIP system, larger fuel tank, fuel cells equipped with oxygen, and hydrogen storage. These vessels are said to be able to remain submerged for longer periods of time than the three existing vessels.