Lol you are absolutely wrong. Li-ion cycle life is typically rated at 99% depth of discharge, rarely at 98%. That means .5 to 1% of maximum capacity without damage.

Deep cycle lead acid is damaged permanently at less than 20% capacity. Manufacturer recommendation is to avoid going below 50%. "Deep cycle" means going below 50% won't immediately destroy your battery... Like most car batteries.

Desulfation can help but will never fully recover a lead acid battery. If you discharge a lead acid battery -any kind- to 1%, it is fucked.