There is the DJVU format for this exact use case, but you’d need to convert them to, say, pdf for many use case. Its also a bit old and perhaps not maintained, soo…
HEIF and other modern video encoders (HEIF=H265) should fare a lot better than JPEG, though.
I would assume the power supply is just not good enough-or isn’t good enough anymore. Rpis are notorious for needing high quality supply for current, preferably the official ones which actually provide 5.1V presumably to account for voltage drop on the cable.