Charging Voltage for a Battery Combiner?

Question:

I have installed a BueSeas ACR. It doesn’t seem to be charging the start battery, the voltage has dropped to 12.9 and the light is blinking.  I can't see what I did wrong? It appeared to be a simple install, I am open to suggestions.  Thank you.  - Ken

Answer:

A battery combiner will only work (i.e. combine batteries) if there is a 13.2/13.3 charging voltage. Your LED is blinking because the charging voltage of 12.9 is too low.