If 40%, 15% or 44% are all based on the % reading on a solar charge controller, then those are PURELY voltage based and not necessarily reliable. If under load, they read artificially low. If under charge, they are artificially high. You will see them fluctuate even when no loads are applied.
I recommend you completely cease all discharges and get the batteries on an alternate charging source. Do not resume battery use until you confirm the battery exceeds the absorption voltage (typically around 14.4V), holds there at least 2-3 hours, and drops to a float voltage, typically around 13.5V. Your charge controller will lie to you by saying 100% well in advance of a full charge actually being obtained.
You need the following to get that battery fully charged in one day:
- optimal year-round tilt for your latitude.
- panels are exposed to sun from dawn to dusk with no shading
- You get at least 4 "solar" hours. That doesn't mean you get only 4 hours of sun, it means you get the equivalent of 4 hours of "high noon" or max power charging per day. 4 hours in a northern latitude in winter is a stretch.
- Min 600W of panels on an MPPT controller
If you fail to meet one or more of the above, it's unlikely that you're getting sufficient sun.
Remember, the amount of solar energy captured by your panels dictates your daily energy use. The amount of battery you have dictates how long you can go without charging.
It appears that you are likely regularly exceeding your daily allotment of solar energy and are not consistently charging your batteries to TRUE 100%.
The only time a % gauge is meaningful is when it's supplied by a battery monitor that is counting the current in and out of the battery and reporting a % based on the programmed capacity, i.e., a good battery monitor knows that you have a 200Ah battery. When it counts the current used = 20Ah, it reports 90%. It's also programmed with the charge termination criteria, so it rests itself to 100%.
