Comment by Pxtl
I've taken the approach of electrical-taping my USB-chargeable 14500s each to a dummy-battery, since the things I put them in have 2 adjacent slots for series AAs. The voltage is still high (3.somethingV instead of 3V) but they seem to work.
Are those LiFePO4 batteries that cap around 3.6V, or normal lithium ion that cap around 4.2V? I'd be cautious with either kind but especially with the latter.