Posted this on another boating forum I frequent ... thought some info may be valuable ...
The charging voltage is always much higher than the maximum possible or 'usable' voltage. The ideal full power charging voltage for lead acid marine batteries is 14.2 to 14.4 volts (double that for a 24V system). Sometimes one only sees 13.8 to 14 (like on my boat volt meter gauge) but that is more the variability in the accuracy of that measuring instrument.
For the best charge result, one must also wait up to ~2-days for the surface effect from the charging to dissipate; otherwise you're fooling yourself with a false (higher) reading. But if you can get 12.4 to 12.7 from a sealed battery ... post-charge, you're good to go!
Note that 'float', trickle or maintenance chargers only bring batteries up to 13.8 volts ... which is a slow incomplete charge, sulfate deposit building, excessive gassing process and one that results in reduced battery life. If you remember anything here, know that continued use of a float or trickle charger will also eventually ruin a battery. It essentially keeps the battery as a 'boiling' point, which reduces the electrolyte, exposes the plates, and causes them to sulfate.
Any values seen down to 11 volts as the OP saw means that the plates have sulfated and portions of the lead plates are now rendered useless. It may take a charge ... but it won't hold it, which is why you need to wait a day or two to get a good reading.
If one doesn't maintain a good charge (> 12) on a battery within as little as 3-days of a deep discharge, the battery can go bad by sulfating and once they do, those plates are permanently damaged and cannot be recovered.
Battery Sulfating 101:
When a lead-acid battery is discharged a soft lead sulfate material forms on the battery plates. During the battery's recharge, that material is lifted off the plates and recombined into the electrolyte. But if left in a state of discharge the lead sulfate material begins to harden and crystallize, forming deposits a permanent insulating barrier. The accumulation of such deposits - 'sulfation' - is the most destructive process in the life of any lead-acid battery. As the barrier becomes thicker and thicker the battery's ability to accept a charge - or deliver full energy - is diminished. Net result ... you'll need another battery!
Ideally for the best charging results, one should use a hydrometer to measure the specific gravity of the electrolyte, but of course that's only practical if the battery has caps to provide access to the electrolyte.
The charging voltage is always much higher than the maximum possible or 'usable' voltage. The ideal full power charging voltage for lead acid marine batteries is 14.2 to 14.4 volts (double that for a 24V system). Sometimes one only sees 13.8 to 14 (like on my boat volt meter gauge) but that is more the variability in the accuracy of that measuring instrument.
For the best charge result, one must also wait up to ~2-days for the surface effect from the charging to dissipate; otherwise you're fooling yourself with a false (higher) reading. But if you can get 12.4 to 12.7 from a sealed battery ... post-charge, you're good to go!
Note that 'float', trickle or maintenance chargers only bring batteries up to 13.8 volts ... which is a slow incomplete charge, sulfate deposit building, excessive gassing process and one that results in reduced battery life. If you remember anything here, know that continued use of a float or trickle charger will also eventually ruin a battery. It essentially keeps the battery as a 'boiling' point, which reduces the electrolyte, exposes the plates, and causes them to sulfate.
Any values seen down to 11 volts as the OP saw means that the plates have sulfated and portions of the lead plates are now rendered useless. It may take a charge ... but it won't hold it, which is why you need to wait a day or two to get a good reading.
If one doesn't maintain a good charge (> 12) on a battery within as little as 3-days of a deep discharge, the battery can go bad by sulfating and once they do, those plates are permanently damaged and cannot be recovered.
Battery Sulfating 101:
When a lead-acid battery is discharged a soft lead sulfate material forms on the battery plates. During the battery's recharge, that material is lifted off the plates and recombined into the electrolyte. But if left in a state of discharge the lead sulfate material begins to harden and crystallize, forming deposits a permanent insulating barrier. The accumulation of such deposits - 'sulfation' - is the most destructive process in the life of any lead-acid battery. As the barrier becomes thicker and thicker the battery's ability to accept a charge - or deliver full energy - is diminished. Net result ... you'll need another battery!
Ideally for the best charging results, one should use a hydrometer to measure the specific gravity of the electrolyte, but of course that's only practical if the battery has caps to provide access to the electrolyte.
