naturist wrote:
If you plan to charge them off the same charger or to use them together at the same time, they also will need to connect to the charger/house system with the same length/same size cable. If the cable to the new batteries is a different length, the batteries on the longer cable will never charge fully, and will discharge to a different depth than the originals, which will cause problems down the road. From the sounds of it, you will have to do the switchover thing.
That might be true if the second set of batteries was 100 feet further away from the charger and 12ga wire was used. At 20 feet with 8ga wire the voltage drop is going to be only 2.15% or 0.31 volts. Instead of 14.5 volts the voltage will be 14.19 volts and this is not going to make a noticeable difference when charging 12 volt batteries to 12.5 volts.
It is not difficult to be anal about this subject. If a 80 Ah battery is at "only 97%" then you can draw 38.8 amps instead of 40 amps from it with a 50% DOD. Does anyone really think this is of critical importance with an RV application?
