This is a bit risky to respond to, but in the interest of helping, I'll share my personal experience and my opinion.
First, can you verify that you have the newest firmware in your camera? It should be 01.82. You can upgrade the firmware using the desktop app. I believe the original THETAs had more problems charging when the amperage was below 1.5amps. I thought this was largely resolved with the newer THETA cameras.
I believe that the THETA S will not charge below a certain threshold for amps. Previously, this was stated as 1.5 amps (or 1500 ma). This is probably not a hard threshold. I suspect that in certain cases, a 1 amp charger could charge the THETA, but just take longer. However, if it's too low, then it probably won't charge. Thus, my opinion is that the 1 amp charger is too low and doesn't have enough power to charge the battery.
Going above 1.5 amps, I've always assumed that the internal regulator of the THETA could compensate for 2 amps. I've been charging the THETA with external 2amp USB chargers for over over a year and haven't had any problems.
Right now, on my desk, I am charging the THETA with this powered USB hub, which should be outputting 2 amps.
I'm also using this wall charger
The black device (the first one) gives my computer many USB ports. The second device (the white one) is only for charging phones, cameras, tablets. The white one is used my family in the kitchen as a community charging station.