Unfortunaltely for the SAR effort for MAS370, it looks like these batteries (if the June 2014 expiry is correct) are end of life units, meaning that they will not last long beyond their certified 30 Day life.
but we have to read the good news out of it ! if they heard pings with the correct frequency in the current area which started to fade away just after the 30 days limit and are now silent it would be to´much concidence to be something else than really the mh370 blackbox. due to the very limited range of such pings they have now the correct search area to nail down where the wreckage is.
imagine the disaster when they would be some days late here and never hear a ping - they would not know if they are close now or if they are still searchin for the haystack in the whole indian ocean to finally find the needle in it.