I have no idea what the BC means other than its a model designation Redarc uses,
In no way am I saying you can't use alternator and solar at the same time, this will still charge, but.....
In earlier vehicles, many still on the road the standard alternator charged at 13.8V. To properly charge an AGM you need 14.4V and a GEL 14.1V. An under hood wet cell deep cycle is ok for alternator charging. In most caravan installs and in later model 4x4 like mine that don't have the space under hood, the battery is in a confined space or the rear of the vehicle and a sealed battery is needed for safety, so usually AGM or GEL and lately Lithium or Lead Crystal. All of these 4 types need better than alternator charging, to fully charge and give the best cycle life.
As I've noted a 3 stage charger starts in Boost, gradually increasing volts and close to the maximum Amps i.e the Redarc starts at 12V increasing (to Absorption V of 14.5) and close to 20Amps. This continues until the battery is between 80-90% charged.
It then moves to Absorption where the voltage is constant i.e. Redarc is 14.5V and the Amperage gradually reduces. (either for a predetermined time or until the Amps input reduces to below 4A for more than 30 seconds. The charger then moves into Float mode where there is minimum current, but the voltage is held at 13.3V. A battery is usually around 98% charged when it goes into Float mode
This then shows 2 issues. - In older vehicles where the Alternator output is 13.8V an AGM will not charge properly as it can't reach the 14.5V stage. Conversely if you have a later vehicle such as mine where the Alternator regularly outputs 14.5V, my AGM would be in constant Absorption mode and end up gassing off/cooking all the time.
Yes in both instances the battery gets a charge, but in both instances it aint doing the battery much good.
Lithium and Calcium batteries are even more fussy about how they are charged and can be a ticking time bomb if not done correctly.
FYI, if you have a smart charger, Solar, DC-DC or Mains that suits an AGM and or GEL and change to a Lead Crystal, you can use those chargers. If you go Lithium, and your charger does not include them, DON'T use it.