Update!

[JWLV]

Here's some more things to give you a headache. When the sun is out and your batteries are being charged, your voltage reading may be much higher than at night. Thus a full battery during the day at 14.4V will read around 13.8V at night. And thats 100% full, but the voltage reading taken at different times. Also, if you have a significant load on the battery, it'll read 0.5V lower even though the battery is pretty close to 100% full. But as soon as you take the load off, it bounces back to 14.4V or 13.8V.

 

[Spower]

Here's some more things to give you a headache. When the sun is out and your batteries are being charged, your voltage reading may be much higher than at night. Thus a full battery during the day at 14.4V will read around 13.8V at night. And thats 100% full, but the voltage reading taken at different times. Also, if you have a significant load on the battery, it'll read 0.5V lower even though the battery is pretty close to 100% full. But as soon as you take the load off, it bounces back to 14.4V or 13.8V.

That's the problem, mine drops to 13.2(something) at night!!