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Old 11-24-2014, 08:07 AM   #21
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City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 6,511
Thank you psneeld for providing link. I read entire page and feel that, in summation, the quote at bottom is most comprehensive for understanding how to deal with lead-acid batteries…

It has been my successful practice during decades of wet-cell/lead-acid battery use: Don’t let deep cell batts get more than 50% discharged before full recharge (it’s OK to fully recharge at any time before that 50% level is reached). Immediately fully recharge starter batts after each use. As long as left in a fully charged state with electrolyte at correct level and isolated for no draw-down occurring… It’s OK to let batts of either type stand unattended (i.e. no charging at all) for up to six months. Climate conditions can have effect on several items regarding charging/using/letting-stand for any batts.

Credit:Following excerpt is from website: “Battery University”


Watering is the single most important step in maintaining a flooded lead acid battery, a requirement that is all to often neglected. The frequency of watering depends on usage, charge method and operating temperature. A new battery should be checked every few weeks to determine the watering requirement. This prevents the electrolyte from falling below the plates. Avoid exposed plates at all times, as this will sustain damage, leading to reduced capacity and lower performance.
Exposed plates will sustain damage, leading to reduced capacity and lower performance. If the plates are exposed, immediately fill the battery with distilled or de-ionized water to cover the plates, and then apply a charge. Do not fill to the correct level before charging as this could cause an overflow during charging. Always top up to the desired level after charging. Never add electrolyte as this upsets the specific gravity and induces rapid corrosion. Watering systems eliminate low electrolyte levels by automatically adding the right amount of water.
Simple Guidelines for Charging Lead Acid Batteries
  • Charge in a well-ventilated area. Hydrogen gas generated during charging is explosive. Please see Health Concerns with Batteries.
  • Choose the appropriate charge program for flooded, gel and AGM batteries. Check manufacturer’s specifications on recommended voltage thresholds.
  • Charge lead acid batteries after each use to prevent sulfation. Do not store on low charge.
  • The plates of flooded batteries must always be fully submerged in electrolyte. Fill battery with distilled or de-ionized water to cover the plates if low. Tap water may be acceptable in some regions. Never add electrolyte.
  • Fill water level to designated level after charging. Overfilling when the battery is empty can cause acid spillage.
  • Formation of gas bubbles in a flooded lead acid indicates that the battery is reaching full state-of-charge (hydrogen on negative plate and oxygen on positive plate).
  • Reduce float charge if the ambient temperature is higher than 29C (85F).
  • Do not allow a lead acid to freeze. An empty battery freezes sooner than one that is fully charged. Never charge a frozen battery.
  • Do not charge at temperatures above 49C (120F).

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