I have usb ports that I use for “critical” stuff like my ipad and phone, so they have essentially unlimited battery life. Not sure if installing usb power outlets is an option for you, but might be something to consider. Otherwise, as Dan suggested, the external batteries are cheap and work well. Just buy some long usb cables so that you can secure the batteries wherever you like.
I am using this one but can’t really garantee it’s free of interferences.
https://www.amazon.fr/Chargeur-Voiture-Adaptateur-Allume-Cigare-Samsung/dp/B09STZ1V86
But for charging perspectives, it’s quite powerfull (on 12V car socket, able to maintain load on Ipad air 4, Iphone 11 and a galaxy tab).
It is also a bit longer and not difficult to remove, whereas the previous anker (I have it also) is good in tterms of power, but very hard to remove once in place.
I had two iPad Mini 4’s with poor battery performance, and discussed with Apple’s “Genius Walk-in” at their Brighton UK outfit who offered replacements (same model) at £285 with 3-month guarantee (or was it £385?) , as they don’t offer battery replacements.
Amazon UK offer “refurbished” iPad Mini4 at around £200 Sterling, with a 12-month warranty.
I took the risk of using an eBay (UK) outfit (Repairsonline) who replaced both at £35 Sterling each, next-day service. Apple checked the batteries and confirmed they were OK. Repairsonline also replace iPad 2 batteries at £25 Sterling. (iPad 2 useless for aviation unless you have an external Bluetooth GPS – remember those?).
Apparently there is a risk of wrecking the screen on iPad Mini replacements, which is maybe why Apple don’t offer the option.
I’ve had a Mini 4 for 6 years, and the few times I forgot my 12V charger, or didn’t bother plugging it for short flights, I could easily get 4-5 hours with the built-in GPS on and usually fairly high screen brightness. A good trick is to go to airplane mode, it turns LTE/wifi/BT off, but GPS reception is still on. Also useful for following the flight/procedures when flying commercial.
I recently upgraded to a Mini 6, but have not flown long trips with it yet. I have a few coming up within a few weeks, will report back on my findings.
For the normal stuff like apps/browsing/games the battery lasts clearly quite much longer than the 4.
