No, you should NOT fully discharge a Lead-Acid battery. The normal reason for wanting to fully discharge a battery is because some batteries have a so-called "memory effect" - old NiCd cells are notorious for this. But Lead-Acid does NOT suffer from this effect.
Let's take it further and recognize that starter and deep cycle lead-acid batteries are not the same (although neither need to be completely discharged before re-charging). No, you should NOT fully discharge a Lead-Acid battery.
Proper maintenance of sealed lead-acid batteries involves regular charging and discharging cycles, keeping the battery clean and dry, and avoiding exposure to extreme temperatures. It is also important to check the battery’s voltage regularly and to replace it when necessary. What is the charging and discharging process of lead acid battery?
Can I recharge a completely dead sealed lead acid battery? Sealed Lead Acid batteries fall under the category of rechargeable batteries and if they are ignored, not charged after use, not charged properly or have reached the end of their intended life span, they are done.
Myth: The worst thing you can do is overcharge a lead acid battery. Fact: The worst thing you can do is under-charge a lead acid battery. Regularly under-charging a battery will result in sulfation with permanent loss of capacity and plate corrosion rates upwards of 25x normal.
The time it takes to discharge a sealed lead-acid battery can vary depending on the load and the battery’s capacity. It is important to monitor the battery’s voltage during the discharge process to ensure that it does not drop below the recommended threshold.