Re- Li-Poly batteries.....the technology is well-established in the model helicopter field, where flight-times of 10 minutes of wild 3-d,hurling ~ 6 lb of battery and machine around the sky is commonplace.
The prices are nowhere near as outlandish as those i've seen bandied about....fully automatic balancing-chargers are available at reasonable prices as well.
Re-Insurance.....in the UK,at least, we have the "unfair contract-terms act" basically, if your "unapproved " mod. or addition did not materially affect the claim,or the basis of it, the insurer couldn't argue and refuse to pay.....already well-proven in other fields- in the motor-trade,an insurer was trying to evade liability, because an aftermarket branded part had been used..... the claimant threatened to inform the parts company of the libellous slur on the quality and merchantability of their product.....claim settled.
In this instance, you have the slothful dead-hand of "jobsworths" (EASA)to contend with...usually all these outfits are several years behind "real-world" developments. If I was convinced that something WOULD enhance my safety, security and chances of survival, I'd be inclined to have professional appraisal to confirm and then go ahead.....it would be a brave or foolhardy "jobsworth" who prosecuted you for sidestepping their failure to discharge their duty of care to YOU, the person they SHOULD be protecting.
Lambs will always go to the slaughter,fools will always comply blindly with idiotic rules.
Sounds like the Cloggies, like the Frogs, take a pragmatic approach and get on with it. good for them.