"An incorrectly spec'd battery turned out to be the cause of that little problem. "

Right,

I will check that! Thanx.

I am reminded of, oh must be nearly 30 years ago, called out to a Merc diesel (Non-start) Dead battery! Customer complained that it was a new one recently obtained via a local suppliers. Then I took a "Double take"

The "New" battery was located sideways across one end of the battery tray! the earth terminal had been stretched right across the tray to reach it!

Of course it was toast!

One correct (and considerably more expensive) new battery later and everything was hunky dory.