The use case for this is to charge the battery during the day and discharge it during the night. It is not for seasonal energy storage. There are no batteries that can be used for seasonal storage, nothing comes within a factor of 100 of being economical. But batteries for seasonal storage requires very few cycles, one per year. This battery here can go through many thousands of cycles. If you don't use it for daily storage, you are paying for something you don't need.
When they are at full charge, they have H2 at 300PSI. Assuming they spend a significant fraction of a day at full-charge, after 10 years they will have totaled a significant fraction of 10 years at 300PSI.
GP's question is "Will the H2 migrate through the pressure tank after such a long time?"