I would suggest that the ULBs requirements are:
Detection Range At least 25 nautical miles in open ocean
Battery Life At least 6 months, possibly by reducing number of pulses and using smart transponder that does not go into regular short location signals until it receives a search request sonar signal
Encoded Location Signals The signals from the ULBs should be encoded with airframe ID, their position (last GPS position of the aircraft) and their depth in the water.
These requirements appear to be asking too much and all that is being offered is a slightly longer life battery.
Well then you will need a unit that's about 4 times as large to give more power output and longivity. But 25NM range: dream on unless you're talking of equipment capable of transmitting to submarines which is massive i.e Rugby.