hi NORTHO
yes it's a bizarre prob isn't it, and f... frustrating...
the help I got on the forum was handy. According to 1 of the members, he explaines that if the batt was on the way out, well, when the parts iunder the bonnet get very hot, they resist better to electricity, that's not good for our problem. obviously, if the batt is tired, it will have greater difficulty in supplying the engine with electricity. i guess.
to solve my heat problems, I started by changing my coolant liquid to nice new one, I also changed my oil and oil filetr, and even in traffic it hardly eats up.
The new battery was the biggest imnprovment: The starter motor spins much energetically, and therefor the car always starts well.
On the french forum, i also talked to some1 who explained that: is starter is on the way out, and to compensate that, he changed his batt. A solution but can be only temporary...maybe that is why u encountered problems, after, even with new batt.
good luck and let me know the outcome.
pjb