Simply reaching 15 volts does not tell you your battery is charged. I am a marine service technician and have been for 40 years. Electrical systems and electronics are my specialty. I deal with complex boat systems every day, or at least I use to. Your battery is fully charged when the amp hours you have taken out of the battery are replaced. Not when the voltage reaches 15 volts. A charger will provide about 14.4 volts and the amps will depend on the size of the charger. A 10 amp charger will only put out 10 amps for a short period of time, then it will back off as the battery get closer to a charge until it reaches the float stage. By simply charging each day until you reach 15 volts, your going to ruin those batteries in short order. If you use, lets say 100 amp hours during normal usage, you will need to charge the batteries until those 100 amp hours have been replaced. In order to charge a wet cell battery, voltage need to be around 14.5 volts. BUT, the battery isn't fully charged until those 100 amp hours are put back. How long that takes depends on the charger. That 10 amp charge will take longer than 10 hours to replace the 100 amp hours used because it does not charge at 10 amps all the time. I see customers all the time that want to know why their new batteries fail in a year. It is always because of improper charging. Every time you don't fully charge a battery bank, you reduce the life of every battery in the bank. It just isn't as simple as reaching a certain voltage point, although the voltage state is important in getting the batteries to full charge. Chuck
