This doesn’t sound entirely right to me. lead acid batteries do get damaged by deep discharges

even “deep cycle” lead acid batteries aren’t supposed to go to full discharge. from https://www.solar-electric.com/learning-center/deep-cycle-ba...

> Deep cycle batteries are designed to be discharged down as much as 80% time after time and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.

It's not. Even a single complete discharge event is often if not usually enough to kill the performance of a lead-acid battery not intended for deep cycle.

I'd say dozens of times in my adult life I've dealt with and recovered lead acid batteries that were completely discharged due to the headlights left on or similar.

Deep cycling performance depends on the battery chemistry. Most cars in the US use a type of lead-acid battery that can't be deep cycled even a single time without serious risk of damage to the cell. I would assume this is true of any lead-acid battery not intended for deep cycling everywhere else in the world too as it adds significant cost to battery.

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.