Most solar controllers default at 13.7v trickle charge for 12v battery charging, but batteries require around 14.1-14.5v to top off that last 5% for a true fully charged battery. Someone might lower that number not knowing and thinking it's too much for a 12v battery, and others assume the manufacturer would know best. Many people are told that your battery at full is 12.7v sitting and a 13.7 trickle will only charge about that high, however my batteries new showed 12.9v fully charged and I'm getting 13v true full charge with my solar by changing the default charge to 14.4v. The last 5% charge is important because it gives the highest amount of AH and helps to season your battery for best depth of storage hours. Some youtube how to vids recommend setting the default to 14.1v, others in forums have set theirs to 14.8v no problem. To be safe I used the parameters of a typical trickle charger and used the 14.4v figure and went from top charge of 12.6-12.7v to 12.9-13v true full charge.