Reluctant to turn over

Returned home in my '95 T5 wagon after a long trip the other day (1,500 ks) during which the vehicle ran faultlessly. I went to start it a couple of days later and it seemed the battery had gone flat as the engine really struggled to turn over and it would not fire. After a few goes it just would not turn-over at all and I thought I could hear a chattering sound (solenoid or main relay???) Suspecting the battery had reached the end of its useful life I purchased another heavy duty battery but it hasn't made any difference at all. I'm starting to believe there may be a fault in the starter circuit as I do not feel that either a lack of spark or fuel would cause the engine to labour when turning-over. There has been no indication of any impending problem; simply it was switched off one day in apparently perfect condition and struggled to turn-over a couple of days later. The T5 always fired up instantaneously so this problem has me really puzzled as well as making me more than a little bit bit miffed. Any ideas out there??

First check all the main (thick) cables from the battery to both ground and the starter motor for poor connections, also check the cable from the engine to the chassis ground/ battery negative.

No start 

No start