An old Standard Horizon took a battery pack that was no longer available so I sent the pack to a guy that advertises online, who replaced all ones in the pack with new and for several years after that it worked like new; actually better then the new water proof ones. When I asked the people at the SH booth at a boat show why their old ones sounded better on the receiving end the reply put the blame on what they had to do to the built in microphones to keep them water proof.
A few months ago I ordered a pair of aftermarket battery packs for my 14 year old SH… from WM of all places. They work good as the original.