Power cuts out when pump runs (on DC)

D MAX wrote:
On DC (2 x 6V) lights are good, power shows full (also metered at batteries 13ish). When the water pump kicks on it dramatically slows down,....Checked the voltage at the batteries while this happens and it shows a slight drop. On shore power no problems at all.

I need clarification on this.

"On DC". Does that mean on batteries alone without the converter running? 13ish is not the resting voltage of any battery, so it sounds as if the converter is on, but then later you say..

"On shore power..." (which runs the converter).

thanks