The problem I had (have?) is it not starting up unless ac power connected.
As a slight aside since a 24 hours charge (see below the topic I started) I have charged it twice for an hour or so just to get back to 80% and like today it started fine.
More info here
There are three main threads as far as I know, this, mine above and one or two more on CMOS inc this…
In my thread above I note the problem I had, the eventual “solution” and how I am progressing day to day whilst waiting a month before doing a 24 hour plus charge again.