Turns out it's fine, it charges to 6/7 bars quite happily if I head down any kind of hill. Our trip mpg is typically around mid 60's for our ultra-urban, flat, 5 mile commute. Even if that's 10% out on I
it's accuracy, I'm still more than happy with that. When monitoring the hybrid battery activity is seems like we use from EV output quite a bit, to the degree that our battery level rarely gets above half way. Anyway, I'm content now that it works properly.
In terms of hybrid battery longevity under this kind of useage, we'll just need to wait and see I suppose. Thanks for everyone who got back to me.