I am dubious of rechargeables. Yeah, phone batteries are pretty reliable but I like having primaries on hand that can be instantly swapped. For one thing lithium primaries are much lighter than Li-Ion batteries. And swapping out primaries if immensely faster than charging from a USB pack. And again, my phone is not ruggedized nor remotely waterproof.

I realize mine is not a popular opinion but it's pretty firmly set in my mind.
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“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman