I have a request - please bring back the BLUE icon for push notifications, it's much more noticeable. The most recent Android update has switched it to white, where it blends in with other notifications.

Correction, I'm using the Arlo-compatible (longer positive button) Eastshines in my Argus:
https://www.amazon.com/Battery-EASTSHINE-E07-Rechargeable-Flashlight/dp/B01CHX06YC

These seem to perform fairly well, but (based on my experience so far) at room temperature, they will be flat dead within 12 hours or so of receiving the low battery warning (that's with one or two camera activations). They have a protection circuit which did not appear to be tripped, which suggests to me that the camera may not be capable of over-discharging a 16340 battery. So, as long as you're using a QUALITY charger (check out HKJ's Li-ion charger reviews: http://lygte-info.dk/info/roundCellChargerIndex%20UK.html), you may not really HAVE to use protected 16340s, which would open up quite a lot of high quality 16340 options. Mountain Electronics is a reputable place to shop for unprotected cells (the protected 16340s they sell will NOT fit (17360 or 17370 would probably be accurate for those), so don't bother. A little extra diameter (17 vs 16 mm) doesn't cause any problems in the Argus.

Same here with the Android app for my Argus.

The flashlight community often uses small neodymium magnet discs to extend the positive button contact. I suspect those who are having contact issues simply need a longer positive button for the battery to allow it to reach the camera contact. However, given the very tight fit I've observed for my Argus (I'm using Evershines designed for the Arlo camera), a magnet may not stay put or could even be too thick (1 mm seems to be the thinnest you can get). Aluminum foil can also work, just be careful it doesn't short anything out.

As was already mentioned, any RCR123A should otherwise work as long as it's not too long, in good health and charged (fully charged voltage should be 4.2V under no load). I suggest you buy RCR123As that will work in the Netgear Arlo camera (this ensures they won't be too long), and stay away from cheap Li-ion batteries! Note that many protected RCR123As sold for flashlights may be too long. I've found one respected brand of RCR123A (16340) commonly used in flashlights that is way too long to fit the battery slot (Efest protected button top), and several others that (based on the specified measurements) are similar in length. 35 mm seems to be the rough limit, but you often can't trust a sellers dimension specs to be very accurate. Based on my first set of discharged RCR123As, unprotected 16340s may be ok to use (since none of the protection circuits was tripped after the camera shut down) and most of those should fit just fine (the protection circuit adds length to the battery, but prevents over-discharge which can reduce the it's cycle life).