On Thu, 9 Mar 2017 16:14:24 +0000, The Natural Philosopher wrote:

On the basis of advice, I disconnected the battery five days ago
(Sunday), charged it up, and left it disconnected. This morning
(Thursday) I reconnected it; the engine started immediately
without
issue (and the same for multiple subsequent starts).

What do you suggest for the next step in the investigation?

Well you have remade the connections.

It should be fine now as the lost likely explanation was a bad
connection.

Yep, leave it and use as normal for a week or so and see if the
problem returns.

--
Cheers
Dave.