Ouch, completely dead usually kills them. They might come back partially but never really full charge. Is it an agm or a refilliable liquid cell. I understand that sealed agm batts have a small chance of recovery but liquid filliable type once dead they stay that way. I have a deep cycle agm battery for a wheelchair, same size and appearance as my utv battery, that I use around my property to run my lawn sprayer and electric boat motor in my pond. I let it go dead by accident about 6 months back. So dar it seems to have recovered, but until I put a real load on it, I wont know for sure.
