I feel like something is missing here but I don't know what.
Our examples show large JPEGs being loaded in MicroPython no problem. For example this one from our examples is 100kB: https://github.com/pimoroni/pimoroni-pico/blob/main/micropyt...
During testing I worked with many images that were larger than that and never ran into issues either. I think the examples provided are pretty clear and demonstrate how to use the product reasonably.
We focus on MicroPython because the C++ SDK for connectivity is pretty gnarly for most people to work with - it is our intention you should never have to leave MicroPython to use this product.
No idea what the battery issue could be but I've never heard of any problem like that before and we've shipped thousands of this product over the past year. We'd be happy to get the unit back and test it for you if you want - or just replace it!
Please drop me a line if you want to discuss these issues further and I'll do my best to help!