Ignition problem Alphard V6 3L 2003

[vitor]

 Alphard V6 3L 2003 (130k kilometres) petrol + LPG.

 

Had no problems for 7 years but couldn't get it to start while away on holiday. Engine turned over strongly and so many times I thought the battery would go flat (it didn't) but no spark, engine did not flood - no smell of petrol. Greenflag mechanic didn't know what it could be but a 2400A powerpack started it immediately. Worked fine for a couple of days, starting as normal, gave it a couple of good runs then same problem and same solution. Ran it back home 250 miles without stopping, trickle charged overnight, started ok. Battery is not that old and tested ok by garage. Local garage at home says there's no spark and can't figure out what is wrong. HT leads?, need a more powerful battery? Any ideas? PS we are old bods who know zilch about vehicle mechanics or electrics.