logicalmethods, glad to hear the 12v battery replacement solved your car's erratic charging behavior.
1) The 12v battery is the source of most of the problems experienced by the i-MiEV, although it is normally not an issue while the car is charging (because the dc-dc is keeping the 12v at the proper level). Best thing everyone can do is replace that battery after a few years, even though it 'tests' ok. This is especially good to do if there is any history of that particular battery having been deeply discharged one or more times during its lifetime (as often happens with i-MiEVs sitting on dealers' lots).
2) The graph you posted is perfectly normal behavior:
a) The temporary dropout after you started charging is normal, and is believed to be the car's attempt to determine if there is excessive sag in the traction battery voltage when power is removed. This 'timeout' can range from about six minutes to 20 minutes, and can be infuriating if you're trying to recharge the car quickly in order to get on your way.
b) As the battery approaches full charge (fuel gauge displaying 16 bars) the input current decreases, the cells get balanced if needed, and then the input simply cuts off when the charging current drops to a certain level.
Both of these topics are fairly extensively covered in many different posts on this forum.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV