[RedDevil]

I have not had any personal experience with the good people at Bumblebee, but I would trust my life on their opinion - their clients are unanimously satisfied.

The Insight uses NiMH batteries, you can look up the properties of those batteries.
You'll find that overcharging them at a gentle rate (300 mA is about 5% of their hourly capacity) does not harm them much. It does bring the cells in line, if they are unbalanced.

I am experimenting with my parallel buddy pack. I see that even when the buddy pack is feeding it the IMA decides once in a while to top the IMA pack charge. It does its own balancing act, so to say.
After that it gets through a phase where it draws from it pack and recharges in rapid succession. Then it just starts depleting its pack until it reaches a 'normal' state-of-charge (still quite high with the buddy pack).
In short the IMA system tends the pack actively.
Why not trust Honda it does that good enough to not need additional grid charging?

2nd gen Insight batteries failing is new to me. It always was due to 12V battery trouble. Even so, some Insights must have been baking in the desert sun for ages, and we know the NiMH battery chemistry does not like that much; just for that there should be a few bad ones nowadays.

The insights are particularly sensitive to low tire pressure and seem to handle better at tire pressures higher than specified on the door sticker.
That said, it remains a matter of taste. I see no real gains of any kind above 40 PSI, so I keep it round that.

To summarise:
If your Insight has not been parked in desert heat conditions there's little chance you'd get a bad IMA battery anytime soon.
You can grid charge but it is not necessary, you won't gain the investment back.
Air up the tires, that will save you a tankful of gas over every service interval.