OK - got home & the charge light was slowly flashing. Measured voltage across battery terminals with 9V adapter still plugged in: 4.19V.
Disconnected 6V regulator therefore taking the regulator, motor controller board and motors out of the picture. Disconnected boarduino from 5V regulator output therefore, only the battery, charger board, switch and 5V regulator were connected. Hooked up 220 ohm resistor to 5V regulator output. This is the smallest configuration I can arrange for without unsoldering stuff and still be able to put a controlled load on the battery. There should be 23mA going through the resistor when turned on. Add some overhead for LED on the regulator, regulator inefficiency and the battery being at 4V instead of 5 & there is roughly 40 or 50 mA load on the battery - this should run a good day or two on a full charge.
Unplugged the power adapter, started a timer and turned it on.
0 mins 4.19V at battery terminal
1 min 4.06
2 min 4.02
3 min 4.02
6 min 2.75
7 min 2.97
I turned it off.
In response to the above message - I have tried unplugging the battery out from the charger board so that only the 9V power adapter, charger board and battery were connected. Waited for hours.
I think the battery is not charging for some reason.
Also, found that the R6 and R7 are swapped on my board w.r.t. the schematic diagram.
Per the schematic the voltage at THERM should be 40% the voltage at THREF. The way the resistors are on my board, it (mathematically) comes out to 34%. 34 is still in the sweet spot according to the chip's datasheet. Measured the voltages at THREF and THERM & they are indeed at a 34% ratio. I measured the DC voltages at various points on the board and they all look reasonable. Hmm.
The following posts will have pictures.