Originally Posted by jdalrymple
I store my trailer at home on constant shore power.
Just remember to switch the use/store switch to store most of the time.
I move it to "use" a day about every month, if I am not traveling.
This keeps the batteries charged, without the overcharging issue.
By the way, the red LED on the use/store switch will remain lit in the "store" position if the trailer is connected to shore power.
Unfortunately, the stock, constant voltage Parallax converter will never adequately charge a battery....ANY battery using ANY on/off modulation or any other technique. This is why so many batteries fail at such a short use period.
Modern lead acid batteries require 3 charging stages to be fully charged and properly maintained.
The initial 'bulk'
charging stage increases the charging voltage slowly from the initial battery voltage to either the set point of the converter or the pre-programmed voltage of a programmable inverter/charger. The amperage also increases during this initial stage to the maximum output of the device as required by the batteries. Batteries require a voltage here of between 14.2 VDC (AGM) to as high as 14.6 VDC (liquid lead acid).
The second charging stage, or 'absorption'
stage (sometimes called the taper charge) maintains this voltage as the batteries fill, and as they fill, the amperage required to fill them becomes less, so the amperage begins to taper or drop. The closer to 100% the batteries become, the lower the amperage required.
The third charging phase is the 'float'
stage. It is here that the voltage and amperage both are reduced to a level that will maintain the battery at or near 100% state of charge. These voltages are 13.2VDC (AGM) and 13.2-13.4VDC (liquid cells). A battery is generally considered fully charged when the resting
voltage is between 12.8-13.2 VDC.
When the stock converter applies only a 13.6VDC output to the batteries, they never really get full, as the required 14.2-14.6 voltage level is never reached. This leaves the batteries in a perpetual state of diminished charge lower than 100%. Plus, if the batteries ever do approach full charge, they never attain a real 'float' voltage, as 13.6VDC is significantly higher than 13.2-13.4VDC.
0.2-0.4VDC might not seem like a lot, but in terms of battery state of charge, this can mean the difference between 100% capacity (12.8VDC) and 70% capacity (12.6VDC) of the batteries.
And all of this doesn't even begin to discuss the use of temperature compensation to adjust the charging voltages depending on the ambient temperatures of the batteries, which is extremely important as all of the above information is calculated at 25ºC, or 77ºF. That is another topic for another time.