Just connect the battery right next to the heater temporarily to see if the cable is your only problem. They do pull a very large current at startup, so no chance of 0.75mm working well. I have mine running from a power supply, and had to get a 20A unit for it to start sucessfully.
Also make...
The new module is connected directly to the light so there's no way its going to affect the fan! The instructions are obviously only a guide and dont cover the situation you have.
You need to install that module in place of the switch, so that its output connects to the light and the fan, put...
I've lifted and refitted boards just fine that were still new, ie only put down the same week.
Can you just double up the underlay in the dips to bring everything up to the hightest points? I'd not be happy with large voids underneath, that hollow sound and feeling isn't nice on laminate.
You could feed the sockets from one of these in each:
https://shellystore.co.uk/product/shelly-1/
Small enough to fit behind the socket if its a deep back box, the app works well and would give remote control of that socket.
If you fill your car first then go to the jam jar or whatever afterwards they're unlikely to stop the pump, they usually just look at you intially before enabling the pump, and if they see a normal situation, ie a car being filled there will be no trouble?
I also like to use petrol for cleaning...
I'd stick to 30m to avoid building regs with all those trees around etc. I tried to go down that route but they wanted some insane foundations due to the proximity of trees in neighbours gardens combined with clay soil, came to around 30k going into the ground! current building hasn't moved or...
I'd also say to just get a few drill bits, 5 and 7 and get decent quality rather than a cheap full set that has some you'll never use. Just get SDS bits to suit your drill rather than mess around with adapters etc.