"The innards did, however, warm up in a hurry. And half an hour of poking an S6 Edge knocked ten per cent off the battery capacity."
Try doing that on the train from Guildford to Victoria using 4G: You can _watch_ the battery percentage decrease before your eyes (about 1% per minute on a Note4).
"That might be a problem because the S6 no longer offers a removable battery, nor a micro SD card slot. Samsung reckons fast charging mode takes care of the first issue by delivering a promised four hours of use after ten minutes of jolting."
In a word: Bullshit.
Yes, you might get that if you turn on powersave modes but there's no way you'll get 4 hours from a 10minute zap if you're using the full fat 4G experience, even with the S6's slightly larger battery capacity and slightly lower power consumption.
External pattery packs might be one answer (I use that for my note4 rather than changing out batteries) but the number of "Qualcomm Quick Charge 2.0" portable packs on the UK market is a number approximating zero(*).
Until about 2 weeks ago there weren't any car or wallwart QC2.0 devices either, so I had to go through Aliexpress to buy mine.
You _can't_ keep these devices charged up on a standard USB charger, even the 2A ones. They automatically throttle to 600-900mA on 5V and require the special Qualcomm Quickcharge gubbins to bump supply voltage to 7.5/9/12V before allowing higher currents. (You need the Qualcomm charger no matter whether the phone's internals are Snapdragon or Exynos-based)
Older "intellicharge" high current chargers won't work with these phones. They're treated as 1A chargers by the phone.
You also can't keep these phones topped up using Qi under full-use conditions (it works well for parking the phone when you're at a desk, but only provides 5V1A to the phones internals at best). I've tried that already and in the car's Qi holder, had to strip down the running services in order to run CameraAlert+Torque+Autoguard without discharging the battery (NFC dots + Tasker are tres useful for automating this kind of thing)
(*) I see one external QC2.0 pack has finally shown up on Amazon, but at 40 quid for 10,000mAh it's not exactly cheap. Aliexpress to the rescue yet again. (There's virtually no point in buying an external pack smaller than 10,000mAh for this kind of phone or phablet)