in the years since that post I've been watching as these started to emerge, but most of them looked kind of sketchy and fly by night. This made me skeptical as there's fairly complicated circuitry right inside each battery to regulate the 3.7V down to 1.5V, I didn't want "super happy golden time" eBay batteries with the broken English instruction pamphlet burning up my expensive wireless gear.There is a brand I found on Amazon that are Li-Ion AA, they are 3.7v when charging, but deliver 1.5 V, the 3.7 connector is hidden (recessed), I use them to power my IEM… not super cheap, but I have used them for 2 years now… well worth it. IMO
I recently have seen offerings from legit battery companies like eneloop, telling me the tech may have finally arrived. I just this month got a set of Amptorrent AAs and the charger, they look and feel well-designed and so far they work great!
batteries like that stay right at 1.5V for their entire cycle while regular rechargeables or even regular alkalines drop from 1.5V almost immediately, spending most of their cycle at more like 1.2V