The reading for Vbatt is dependent on the +5 voltage readings?

[jimrh]

Forking the discussion from:
Automagic low-battery shutdown for Charlie?

Apparently the micro-controller processor chip is an ATSAMC20J - which is a 32 bit microcontroller with some serious chops!

This is the feature overview from the datasheet:

Operating Conditions
• 2.7V – 5.5V
– -40°C to +125°C, DC to 48 MHz
– -40°C to +85°C, DC to 64 MHz
Core
• Arm® Cortex®-M0+ CPU running at up to 48 MHz or 64 MHz:
– Single-cycle hardware multiplier
– Micro Trace Buffer
– Memory Protection Unit (MPU)
Memories
• 32/64/128/256 KB in-system self-programmable Flash
• 1/2/4/8 KB independent self-programmable Flash for EEPROM emulation
• 4/8/16/32 KB SRAM main memory
System
• Power-on Reset (POR) and Brown-out Detection (BOD)
• Internal and external clock options with 48 MHz to 96 MHz Fractional Digital Phase Locked Loop (FDPLL96M)
• External Interrupt Controller (EIC) (Interrupt pin debouncing is only available in SAM C20/C21 N)
• 16 external interrupts
– Hardware debouncing (only available in SAM C20/C21 N)
• One non-maskable interrupt
• Two-pin Serial Wire Debug (SWD) programming, test, and debugging interface
Low-Power
• Idle and Standby Sleep modes
• SleepWalking peripherals
Peripherals
• Hardware Divide and Square Root Accelerator (DIVAS)
• 12-channel Direct Memory Access Controller (DMAC)
• 12-channel Event System
• Up to eight 16-bit Timer/Counters (TC), configurable as either (see Note):
Note: Maximum and minimum capture is only available in the SAM C21N devices.
– One 16-bit TC with compare/capture channels
– One 8-bit TC with compare/capture channels
– One 32-bit TC with compare/capture channels, by using two TCs
• Two 24-bit and one 16-bit Timer/Counter for Control (TCC), with extended functions:
– Up to eight PWM channels on each 24-bit TCC
– Up to two PWM channels on each 16-bit TCC
– Up to four compare channels with optional complementary output
– Generation of synchronized pulse width modulation (PWM) pattern across port pins
– Deterministic fault protection, fast decay and configurable dead-time between complementary output
– Dithering that increase resolution with up to 5 bit and reduce quantization error
• Frequency Meter (The division reference clock is only available in the SAM C21N)
• 32-bit Real Time Counter (RTC) with clock/calendar function
• Watchdog Timer (WDT)
• CRC-32 generator
• Up to two Controller Area Network (CAN) interfaces in the SAM C21:
– CAN 2.0A/B and CAN-FD (ISO 11898-1:2015)
• Each CAN interface have two selectable pin locations to switch between two external CAN
transceivers (without the need for an external switch)
• Up to eight Serial Communication Interfaces (SERCOM), each configurable to operate as either:
– USART with full-duplex and single-wire half-duplex configuration
– I2C up to 3.4 MHz (Except SERCOM6 and SERCOM7)
– SPI
– LIN host/client
– RS-485
– PMBus
• One Configurable Custom Logic (CCL)
• Up to Two 12-bit, 1 Msps Analog-to-Digital Converter (ADC) with up to 12 channels each (20 unique channels)
– Differential and single-ended input
– Automatic offset and gain error compensation
– Oversampling and decimation in hardware to support 13, 14, 15 or 16-bit resolution
• One 16-bit Sigma-Delta Analog-to-Digital Converter (SDADC) with up to 3 differential channels in the SAM C21
• 10-bit, 350 ksps Digital-to-Analog Converter (DAC) in the SAM C21
• Up to four Analog Comparators (AC) with Window Compare function
• Integrated Temperature Sensor in the SAM C21
• Peripheral Touch Controller (PTC)
– 256-Channel capacitive touch and proximity sensing
I/O
• Up to 84 programmable I/O pins

Damn!  That would be sweet on a broken-out dev board like an Arduino!

I am going to read more and find out what is going on.