A single BCDC charger can charge both an under-bonnet auxiliary battery and a rear or trailer battery, but it is not ideal.
Voltage drop over long cable runs can prevent the rear battery from reaching full charge, and using different battery types risks over- or under-charging. High under-bonnet temperatures also cause the BCDC to reduce output, limiting charge to both batteries.
The best setup is to install a BCDC close to each auxiliary battery, or as a compromise, use an SBI12 isolator for the under-bonnet battery and a BCDC near the rear or trailer battery.
REDARC recommends seeking the support of a qualified auto electrician or technician.
Important
For your safety, REDARC recommends installation by a qualified auto electrician or technician. Our trusted REDNetwork is made up of professional auto electrical businesses certified by REDARC to install the complete of REDARC solutions. Find Your Local Installer
Can I use the BCDC charger to charge my under-bonnet auxiliary battery as well as my fridge battery in the rear of the vehicle (or the slide on camper or the camper trailer)?
Whilst this can be done, it is not as good as having a BCDC charger close to each auxiliary battery you want charged. The reasons for this are:
The BCDC will charge the under-bonnet battery 100% but the voltage drop associated with the long run of cable from there to the battery in other location will mean that battery may take longer to reach 100% charge or may not reach 100% charge if it has a fixed load such as a fridge (unless you use heavy cable).
If the auxiliary battery under the bonnet is a different type from the battery in the other location, it is likely one battery or the other will be either under or over charged. For example if you set the BCDC* to charge the standard flooded battery under the bonnet and you have an AGM or Gel battery in the other location, it may be over charged. Alternatively, if you set the BCDC* to charge the AGM or Gel in the other location, the one under the bonnet may be undercharged.
The BCDC* will work at full capacity up to 55°C ambient. Above that it will de-rate its output as temperature increases such that at 85°C, it will cut back to no charge at all. This is partly to protect itself but more importantly to protect the battery, as batteries can be damaged by being charged 100% in under-bonnet temperatures (especially AGM or Gel batteries).
* If your under-bonnet battery is being protected in this way, the battery in the relatively cool other location is also getting a reduced charge when it could be getting full charge as it is not in the hot environment.
For these reasons, it is far better to have a BCDC close to each auxiliary battery being charged. If you want avoid the cost of two BCDC* chargers, one possible compromise is to have a SBI12 battery isolator for the under-bonnet battery and a BCDC charger close to the battery in the other location.