Not quite sure what to make of this response from NOCO:
Thank you for contacting NOCO support. The charger is protected with an inline fuse, and if it senses voltage from the alternator it would go into error and flash LEDs. We recommend removing the charger from the battery prior to ignition to prevent a possible back surge.
It's a CYA lawyer-speak boilerplate tech support script. Hand-holding nannycrap for the uninitiated.
First of all, that statement implies that the fuse has something to do with sensing voltage and entering an error state. It doesn't. If you try to feed it too much power from the battery end, the fuse blows.
For instance hooking a 12v charger to a 24v battery would normally do it. Except if we're talking about the NOCO 26000 - that's a 12v or 24v charger, so it's going to take a lot more than 24v to blow the fuse.
Second, it can't "sense voltage from the alternator" - it's hooked to the battery. All it can possibly sense is "voltage at battery connection is X".
If the voltage regulator causes the alternator to supply some voltage that is more than the NOCO expects to see at the battery connection then it could "go into error and flash LEDs".
For instance if the voltage regulator is running the alternator at 14.8v, but you have the charger set to "12v NORM" which is capped at 14.5v; when it sees >14.5v on the battery side, it will error out.
As to the "back surge" from starting the engine...the bloody thing has a jump charge mode. If they actually expect that no one will accidently leave it connected when late for work and trying to get a car with a dead battery started, then that's just crappy engineering. But they aren't crappy engineers. They know it's quite likely that charger will still be connected when the engine starts.
And even if it was, the "back surge" from a 12v system won't be enough to blow up a charger that can do 29.6v (in "24v COLD/AGM" mode).
AND! It comes with the bolt-on wiring to permanently hard-wire it to the battery full-time. [Edit: Hrmm...looking at the pics again...maybe not] What? They expect someone is going to unbolt that every time before they start the engine?
And finally, no they do not "recommend removing the charger from the battery prior to ignition to prevent a possible back surge".
In the manual, the instructions for using the jump charge don't say anyrhing about disconnecting it before starting the engine.
So no, that line about disconnecting before starting is complete BS.