DrMichael I have no idea! My best guess would be some sort of LIPO pouch but I don't really want to tear down my unit just to answer this question. If you really need to know this, I'd suggest asking Customer service or the manufacturer, rather than asking in a user forum like this. In practice, I keep the unit plugged in (micro-usb) while using it for PCB inspection, etc.so I can capture recordings on my desktop and just push the power button to use the internal battery when I'm up trying to support my aging eyesight when reading component markings on ICs etc. Why do semi-conductor manufacturers think it's smart to have barely legible markings? One day these designers will get older (hopefully so, when you consider the alternative!) and Karma will kick in. Agism has already taken over the graphics design sector. Let's keep it out of electronics!

DrMichael Note: I do not have permission to post links here so I can only give you an overview in this response. 1) This is an ESP-C3-12F-Kit which is a RISC V chip. Google "ESP-C3-12F-Kit" for lots of "how to" information. 2) The pin-out is given on the original Banggood listing. 3) I cannot understand why you were able even to blink LEDs if you were compiling for the D0WDQ6; it shouldn't work! 4) ST7735 or ILI9488 are straightforward since the ESP32 family are natively 3.3V 5) I'd suggest you head over to the espressif site and follow the instructions for setting up the Arduino IDE and try some of the examples there. Once you are on top of the basics, ask this community again about any specific issues you encounter.

DrMichael You connect to the out+ and out- pads. You can connect a switch to the two SW pads to turn the output on or off, or just bridge them to permanently enable the output. The output as supplied is always 5V but id hackable; do a google search for hoe to do this.

DrMichael From the TI datasheet ...Humidity: operating range 0%RH to 100%RH (accuracy -2%RH)Temperature range: -40C to 125C (accuracy - 0.2C)

DrMichael I'd suggest you ask this question of customer service or the seller. (This forum is for those of us who have purchased the item to try to help others considering purchase by answering product-related questions).

DrMichael According to the listing, it is IP65 waterproof. The unit I bought appears to have some sort of conformal coating over the solar panel so it should by OK protecting against lop pressure water ingress.

DrMichael I'd suggest you ask Customer service this question. This forum directs queries to people who have bought this item so they can respond based on their experience. I can attempt to answer product related questions, but I cannot speak for BG on their stocking policy.

DrMichael First, I only got this tablet two days ago, so I have limited experience with it. Second, I don't use it with a sim, just on Wi-Fi. Having said that, I'd expect it to work fine as a phone; I just prefer to use a smaller phone that will fit in my shirt pocket. Similarly, I don't use WhatsApp (I find their terms and privacy policy unacceptable) so I have no experience with it. Nevertheless, I can see no reason why it wouldn't work. I am sorry I can't be more helpful, but I am a bit of a privacy freak and one of those strange people that actually reads the terms of online services rather than just saying "agree".