Once again you are a fountain of knowledge which i am grateful for. I wasn't aware that the main batteries were very costly. I have an old SLK ( what a great car btw) and a battery about £70. So the new breed are hundreds?
I agree that one can get stuck in a time warp and reject modernity and 'improvements in technology' but perhaps it is too early to tell perhaps. As an aside, how great being able to have leather seats as an option in my HRV in 2001. From memory £500. Just come to me that the cloth seat had a cigarette burn and it was the salesman who suggested the leather. Still in great shape, which cloth wouldn't be. The Jazz had half leather and wasn't great quality and i prefer 100% of one or other. The Merc leather in 2 tone is something to behold. Funny but the Honda dealership is on a hill and the Jazz toiled going up. When we drove off later in the Merc it took it in its stride!
Oh dear I seem to have put my foot in it and need to put the battery cost for Hybrids and EV's into context .
The 12v battery is an ordinary lead acid battery, ancient technology as used by most cars .Like all cars this may need replacing every few years, for £70 or less.
The High voltage battery used for traction in EV mode in Hybrids and EV's is high tech, and very expensive. Its the main reason these cars are so expensive when new. But this battery is designed to last the life of the car. Its no more likely to need a new HV battery than a relatively new car would need a complete brand new engine fitted at main dealer prices. (but if it did the cost might be similar

) On the plus side Hybrids related mechanicals are simple and reliable and far less likely to need expensive repairs to clutch , gearbox, engine etc that often send cars to the scrapyard before their time.
For those who might be concerned about running a mk4 hybrid in the future when the car reaches its teenage years . If the battery starts to show its age and needs replacement there are specialists already appearing able to recycle and renovate EV batteries at more realistic cost .Either good used ones from scrapped cars , or rebuilding batteries using new cells. The cost might be more akin to getting a clutch or gearbox replaced rather than a 12v battery.

Unwelcome but viable if it extends the life of the car. On the plus side you shouldn't also face the cost of a new clutch etc, and ,as another post illustrates, may have already saved £3K + in petrol costs.
I am surprised it was sluggish up hill. If you give it plenty of throttle it should climb well enough, but may get noisier than usual for a short while.