Jorge, I have had batteries in my sailboats for years, and I always used a solar charger to keep them topped off between short sails, depending upon a charger for extended use replenishment. To know your battery state, buy Radio Shack's cheapest digital voltmeter that reads DC Volts to the hundredths, then use this chart I made up which gives you a fairly accurate idea of the percentage of charge remaining. Since lead acid batteries have a cell voltage of 2.10 volts at full charge, you'll note that a fully charged 12 volt battery (six cells) has 12.6 volts. If your solar charger ever charges over 14.66 volts, get a regulator for it, or you will damage it by overcharging. TWELVE VOLT BATTERY VOLTAGES & PERCENTS 14.66 - MAX 12.60 - 100 12.50 - 90 12.40 - 80 12.33 - 70 12.27 - 60 12.17 - 50 12.07 - 40 11.97 - 30 11.87 - 20 11.50 - 10 10.50 - 0% I hope this helps you out, perhaps others, too. John Butler theoldcat@cox.net M15 "Rejoyce"