Many newcomers to the Renewable Energy world are very concerned about getting the voltage right when charging their batteries, but this is not as important as you would think.
The battery will always try to keep the voltage going into it, at the voltage level of the battery itself. The battery will be sitting at 13 volts, and your Wind/Solar power will be 22 volts open circuit. As soon as you connect your open circuit Wind/Solar power to the battery, POOF ,everything is now running at 13 volts. It pretty much doesn't matter what voltage you want to charge the battery with, Your genny may be making 65 volts open, but connect it to the battery and then everything is at the battery voltage.
What happens to all that extra voltage? It's converted to amps. If using Wind power this is where you start to worry about your stator burning up. Once your Wind or Solar reaches Cut-In (battery voltage) the measured volts will be the battery voltage which should be increasing slowly as it is charging. The power will go up past cut-in and the voltage doesn't increase, but the amps do. Under most circumstances you don't have to worry about the voltage of the device you are connecting to the battery, your worry will be with the ability of the charging device to deliver the Amps without burning up.
When Charging a battery try to keep the current going in to less then 10% of the capacity of the battery. For Example: a 100 amphour battery should be charging at 10 amps or less.
Your battery's voltage readings will change depending on how it is being used. It may be sitting at 12.36 volts when it is not being used at all, then jump up to 13.30 volts when you are trying to charge it, or drop down to 12.25 volts when you are discharging it. These are not exact numbers and your voltage readings will be different depending on how hard you are charging or discharging the battery. Here is a chart that will give you an idea about how this works.
State of Charge (SOC) Chart: Lead Acid Battery
% of Charge Charging At Rest Discharging
100 - - - - - - - - - 14.75 - - - - - - 12.70 - - - - - - 12.50
90 - - - - - - - - - - 13.75 - - - - - - 12.58 - - - - - - 12.40
80 - - - - - - - - - - 13.45 - - - - - - 12.46 - - - - - - 12.30
70 - - - - - - - - - - 13.30 - - - - - - 12.36 - - - - - - 12.25
60 - - - - - - - - - - 13.20 - - - - - - 12.28 - - - - - - 12.15
50 - - - - - - - - - - 13.10 - - - - - - 12.20 - - - - - - 12.00
40 - - - - - - - - - - 12.95 - - - - - - 12.12 - - - - - - 11.90
30 - - - - - - - - - - 12.75 - - - - - - 12.02 - - - - - - 11.70
20 - - - - - - - - - - 12.55 - - - - - - 11.88 - - - - - - 11.50
10 - - - - - - - - - - 12.25 - - - - - - 11.72 - - - - - - 11.25
http://solarjohn.blogspot.com/2007/03/measuring-battery-state-of-charge.html
