Battery voltage is such a difficult topic to explain in black and white because there can be many different variances that contribute to voltage. Below I have provided a helpful reference chart to show what percentage your battery is at based on the voltage shown.
Please note: the chart is not 100% accurate, but it will give you a rough guide of where you are at with your state of charge. To get the best reading possible, the battery would have to be sitting idle (not charging or discharging). For example, your battery is charging from solar during the day, the voltage percentage would be higher than on the chart. Conversely, if your battery is discharging because the pump or the lights are on, the percentage would be lower than on the chart.
Ideally, voltage should be kept around 100% to ensure you get the most life out of your battery.
Keep in mind, a battery can be over-charged and should never go above 14.8v. This is where it gets a bit complicated: when charging a battery it can "float" at 13.6v, and then jump up to 14.8v, but once it is fully charged it will go back down to 13.6v. So, don't be alarmed if it goes to 14.8v temporarily (a couple hours), but if it stays there permanently or goes any higher than 14.8v it can damage the battery.
I could go on and on about battery voltage and the different scenarios that might affect it, but what I'm trying to do here is explain it as simply as possible and give some clarity on what the numbers mean.