Neuro, please, you 're better than this. Every Canon camera comes with a fully functioning, non-counterfeit battery (even if it *can* trip Canon's no-fakes-protection). You can always use that for spares - I do. There's your backup. But my four main batteries are aftermarket, averaging less than $15 a piece.
I used third parties for over a decade, never a problem. You really should ignore that, as a scientist of your stature would steer well clear of generalisations based on hearsay, as you did in your previous post. By the way, by that reasoning, all Canons are unreliable, too. An even dumber argument is to regard the price of batts relative to the price of the camera. You only buy expensive petrol for your expensive car?
And "I suspect most people would consider that a significant risk"? WTF? That *is* fud, and a fallacy. Posts like these take away my appetite for this forum. And I KNOW you're cleverer than this. I'm with Marsu - in suspecting the fud has sunk in, at least - and out of here. Don't bother convincing me you were making sense - you're not and you know it.
Have you ever taken more shots in one day than a single battery allows? If not, lucky you. If so, how good is one
'fully functioning, non-counterfeit battery' as a backup?
Ahhh, so the reports of 3rd party batteries failing to register with the camera and/or becoming incompatible with the Canon LC-E6 charger are baseless lies? Or they're true, but there's just no chance of it actually happening? Or if it does happen, there's no risk of not having enough batteries to finish the shoot/day/trip? Many event shooters have at least one battery charging during the event. Personally, when on vacation I leave a battery (or batteries) in the charger in the hotel room, so I can swap in freshly-charged at the end of the day, before heading out at night. If you're shooting in the cold, you get far fewer shots per charge than in temperate climates.
It's in Canon's best interest to ensure their OEM batteries retain full compatibility with their cameras, whereas they have no such motivation with 3rd parties (and, it could be argued, it's better for Canon if they engineer a planned failure of a non-OEM product). There's always a risk any product will fail. That risk is higher with a 3rd party battery, as shown by dgatwood's post, but 3rd party batteries are cheaper. So, like many things in life, everyone can make their own decision about how much risk they're willing to tolerate vs. how much money they'll save. To you, the benefit of the cost savings outweighed the additional risk. For me, if spending an extra $30-40 mitigates that risk, even a little bit, that's money well spent.
Sorry you're losing your appetite - I KNOW the truth sometimes gives people indigestion.