Flooded cell batteries have to be one of the most neglected components in any low voltage / high amperage system. FC batteries that are discharged are for a reason and one needs to determine why before attempting to revive them and FC batteries have a finite life as well. I depend on my FC batteries to start my ag equipment and why they get replaced on a regular basis or when they load test marginally. Never had any FC battery last more than 5 years. While an aged FC battery may test good, a load test will almost always show it's marginal and oxidation in the connections can and will degrade the output amperage, always. I keep all my connections clean and bright and coat them with a compound that resists oxidation as well.
One thing I do with ALL my FC starting batteries in my farm tractors is, I take them out of circuit when the tractors are stored over winter. My starting batteries ALL have physical disconnects on the NEGATIVE side (post) on them and I take them out of circuit when in storage. That eliminates any parasitic draw and FC batteries will discharge is minimal at best.
I don't own any boost chargers and don't plan on ever owning one other than the microprocesser controlled 'trickle' chargers I have on my truck and side by side that sleep in the garage all winter and I only use Battery Tenders (brand) or Yuhasa tenders.
If a FC battery is dead, there is a reason why and you need to determine that and correct it before 'boosting' any FC battery. Usually it's because the battery has reached it's limit of useful life. That applies to the newer AGM's as well which are really FC batteries anyway but the electrolyte is suspended in a glass mat instead of just floating around the plates. Same chemical action applies, same lifespan applies as well.
