Thats not a power problem i wouldnt of thought mate
If you switched the van on and the voltage shot up then your split charger is fine and the connections seem ok...
No power at the pump but getting over 13V suggests to me a pump or controller problem mate...spruce will know more though
I found a problem with a mates system doing this. It was not only battery charge related but when we recalibrated the controller half of the problem went away.
If the battery showed 12.6v after it has stood for 4 hours then the battery wasn't fully charged. 12.7 and above is fully charged and 12.5v is 75% charged. If it showed that voltage shortly after the engine had stopped, then it would have much less charge as the voltage across the terminals would have dropped further.
We experienced a failure where the pump was cycling, but there was very little flow at the brush. I eventually tracked it down to a faulty Hozelock female stop not opening properly. It was about 4 months old and suddenly developed a problem at around dinner (lunch) time. Starting the engine made no difference to the result.
We have also had similar issues with a hose kinking on the hose reel near the inner spindle. Removing the 100m of hose and relayering it solved that problem for a bit. The final solution for that was to replace the hose as it was stretching too much.
Our last replaced 110 amp battery was replaced as it no longer had the capacity to do a day's work. (From flat it took about a few hours before the charger reported it as fully charged.) When the pumps stopped, starting the engine revived them without any spluttering as there was more amps available from the vans alternator than the 2 pumps required.
At least getting the battery onto a good leisure battery charger is a step forward to identifying the problem.
The is another thread running at the moment where Ian Sheppard has made an excellent point with regard to performance issues we will experience if we let our batteries get too low on charge.
There are some battery manufacturers that quote some very high numbers of discharge and recharge cycles a battery is good for. It gives us the user the impression that this is a quality battery. But the small print shows that these cycles may only be from full to 80% charge and under best performance temperatures. Continually running a battery a 1/2 its full capacity will 'kill' it very quickly.