Consider the following:
1. How much current is the caravan using compared to the current available from the J35 to power loads and charge the battery?
If the caravan is using most of the available current to power the loads, then there will be less current available for charging, so it will take longer to charge the battery and the state of charge graph won’t fill as quickly.
For example, if the J35 / BP35 is powered from the solar input, and solar is providing 6A of current, while the caravan accessories are drawing 5A of current, then there is only 1A of current available to charge the battery.
2. Is there a charge source fitted directly to the battery?
The J35/ BP35 can’t see current flow at the battery if an accessory, such as generator, is connected directly to the battery. If the J35 doesn’t see the current, neither does your battery monitor.
If you are planning on connecting any load direct to battery you should install BMPRO’s BC300 External Shunt + CommLink. The BC300 allows the J35 /BatteryPlus35 and monitor see current flow from sources connected directly to the battery, so you are always correctly informed on the power into and out of your battery.