What happens when you loose coolant due to a busted hose?........hint....no alarm
Look for Aussie product called "engine guard" and see how that operates.
Show make/model of charger along with photos inside and out, as well as both sides of the pc board.
Any close up (for example fuses quoted) should be previewed before posting to ensure clean sharp photos.
Be aware before you even begin, any switchmode type supply repairs are not for beginners...
You will find the ds3231 is an accurate device.
Suggest you build a basic circuit with just the ds3231 and the arduino, upload some basic code and verify via the serial monitor.
Also read intro at top of the forum pages.
Could be a bit tricky for a beginner to fit, even with the correct part.
Perhaps think about using an old usb lead and solder the cables direct to the 4 pins.
Place coils in parallel, use a power supply sufficiently sized for all 6 coils (plus about 50% margin to allow for inrush current).
No idea where you are measuring power or how your connections are made so supply a photo and a pencil sketch of everything.
I would take a guess and say it would not conform with any medical grade certification given the board is a bit of old veroboard type material, bit like a knock-up proto-type.
To quickly verify backblight fault, shine a torch on an angle across the screen.
If you can see any image, it is a backlight problem.
Search Google for common backlight problems on your model monitor.
Used one like this for 30 odd years.......mine goes from 1 to 8 cells. 15v dc supply and simply adjust the current, no voltage adjust necessary.
https://www.electronicecircuits.com/electronic-circuits/ni-mh-ni-cd-adjustable-constant-current-charger/