ULB/ELT

Would you mind explaining the working mechanism of batteries used for under water locator beacon and ELT

The ULB battery is a water activated device. It uses water as a conductor between the outer band and center contact to complete the circuit.
  
     
  
To activate for test, we use a small piece of wire mesh between the two contact points.

We've been installing larger ULB's attached to aircraft frame next to the recorders. The battery is larger and the beacon "pings" at a ≈1/3 slower rate. These are being used on ETOPS (extended range aircraft). I'm sure this addition is in response to Air France 447 which crashed into the Atlantic. The recorder ULB batteries ran out of battery power before the aircraft was located.

The ELT uses a "G" switch to activate the unit. It can also be turned on manually.
  
     
     
 

Mark, taking into account all available commercial products which may be used as ULB battery, would you mind tell me how much the battery cost on average?

I didn't know that are different batteries for a ULB. That is up to the "certified repair station" for those units.

Batteries are not replaced on the line. A new (replacement) unit should come with the proper paperwork to verify it is eligible to installed on an aircraft.

Mark, with regard to AMM pages I have sent just a moment ago:
1-Is G02440 battery different from Dukane 810-2007/k. battery, given it would be put in ULB Dukane model DK120K?
2-do you have any idea on how much aforesaid battery may cost on an average?