I left the tuned to the APRS beacon frequency for most of the afternoon, with its occasional beacon Tx turned on. For APRS you need to turn off the Rx power saver feature (so that sections of packet transmissions are not lost when the receiver circuitry is temporarily cycled off).
At 6:30pm just as I was leaving for the North Shore Amateur Radio Club meeting, the mini-meter on the main display showed full bars. When I got back at 10pm, the radio was apparently off. The radio is supposed to draw 240mA on dual receive mode (as it was). I had the volume turned right down, so I can only imagine this cut the current requirement somewhat. The standard battery is nominally 1100mAh, so I would probably expect to get over 4.6 hours of use in this mode, which I think I did quite easily.
From its supposedly depleted state, I placed the radio on the fast charger and it immediately turned back on. The charger also indicated that it was charging the battery (solid red light). By 2am, the radio was fully charged (according to the steady green light on the charger), so I turned off the radio for the night.
So far then, no repeat of the odd refusal to fast-charge problem I experienced. Maybe the battery is 'normalising'.
Tomorrow I will try operating the radio from its base (which I think is the condition it was in on the occasion that the battery ran down and refused to charge in the fast-charger). It it goes a day or so in use like that, I'll be more inclined to the belief that the bad experience was an aberration and move on!