gotgcoalman wrote:Altransit wrote:That all sounds very logical, if I still had the van, I would be tempted to upgrade the wiring to include a relay, just to see if it cured the poor starting

or,,,,,,,,
second battery to double the CCA

I have the (extra) relay, the powerful 2.7KW Bosch starter motor and a good 12 Volt 74 AH 680A (EN) battery...
Every time I am surprised how good this engine starts!
Again to my knowlidge
There is absolute no need for a second battery if the first one is OK.
You have zero on the double (ca. 1300cca) cranking power of two battery's if the starter motor needs less than 680!
What you do NOT (NOT) need is losing to much tension (VOLTAGE) in the leads and connections to the starter motor and solenoid.
The higher the current, the lower the tension on the end of the cable! (Basic school electricity)
The higher the resistance in the lead (smaller diameter) or the connections, the bigger the loss and the lower the tension, on the end of the cable ( again basic school electricity)
I hope i have all the words right..., obvious I could explain better in my native language.

Never forget to (in)calculate the losses in the negative - (earth) cable, I try to keep them the same size as the positive + for good results.