13.6v

It will get there at that voltage. I am assuming that your 6V batteries are hooked together in series to give you 12 volts.

Yes, 12v bank.

Having seen PD's 13.2, 13.6, 14.4 graph numerous times here, just wondering in 13.2 or 13.6 given enough time (days, weeks ...) can get a battery back to 100%

That will get to where no more amps are going in, which is one notion of "full." But the joke's on you when you check with an hydrometer and see the SG is only "fair" instead of "good." (13.6 is below the "gassing voltage")

To recharge 6s fully, you need to do this:

http://pdf.wholesalesolar.com/battery-folder/charging_instruction_2011_2.pdf

It depends on your batteries condition but at 13.6V I can charge my two 6V batteries from halfway discharged to a full charge in about 36 - 48 hours. At that time the charger changes to the maintenace mode (13.2V). If I use the 14.4V quick charge mode they will charge to 90% in about 6 hours and them take another 12 hours to fully charge at 13.6V. These times are all approximations and assume no devices are pulling current while charging. My batteries are fairly new, purchased late last year.

Check in a week with a hydrometer.

It appears 13.6VDC with a charge capacity of 15-20 AMPS per battery will take 40 hours to attain a 90% State of Charge and a hugh 78 hours to get to 100% State of Charge

Consider this report from PROGRESSIVE DYNAMICS on how it takes different DC VOLTAGE LEVELS to charge a deep cycle 12VDC battery.

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

this is battery science - not many ways around it...

Roy Ken

X2 BFL. 13.6V charge never did much to my batt bank. I think it managed to get them into the 70% SOC range after a few weeks.

Must be a good question when you get five different answers (opinions) so quickly.

My understanding is that an otherwise healthy battery that will no longer accept charge at 13.6 volts is fully charged. The hydrometer always lags though less so approaching full charge, due to how the chemical process functions. However, the electrolyte also stratifies so that it appears by hydrometer not to be at full SG. The purpose of increasing the voltage to induce gassing for a short time is not to make the battery "more full", but to stir the electrolyte until the mix is homogeneous, causing the SG to rise slightly during this time until it reaches a steady state when the mix is complete. Further charging at gassing voltage only causes a need for more watering and plate erosion.

Check out Battery University

Fire away!

13.5 is like grabbing a snack on the go - you won't fall flat on your face right away but living on it is another story entirely. For maintenance, 13.6 is a battery death sentence due to sulfation and stratification.