Repair 12v Camping Style Battery Box

[secondlife]

Hey All.

Looking for a little help in how to locate what may be causing the issue with my Arkpack Battery Box causing it to display approx 0.7V less than the confirmed battery voltage. I have been unable to locate schematics for the unit and have had to delve into the world of digital electronics further than I have previously. My past repairs have not been in the microcontroller space and I am starting to get the feeling this may be the issue here,

First I am making a few assumptions. a) That this device is using a shunt off the main battery supply to determine the voltage and b) given the shunt seems to follow the usual U shaped wire type and its resistance as close as I can tell is correct at 0.1Ohms.

I have checked all the resistors that look like voltage dividers and all check out OK but given it seems the magic is happening on the silicon and I have no idea what pin is for what its hard to know where to from here. I have included a pic of the board for reference but an ideas on next steps would be welcome.

Link to the product: https://www.bcf.com.au/p/ark-arkpak-730-power-battery-box/373115.html

[geggi1]

To me it sounds like it might be that the voltage is measured on the wrong side of a diode.
When a diode is conducting you will have about 0,7V over the junction.
Look at the beefy diodes like D1 and D11 if one of them are in the output path of the battery you have the reason there.

[TheMG]

Is it just me or does the polyfuse (F3) look like it has taken some damage?

[fzabkar]

Is it just me or does the polyfuse (F3) look like it has taken some damage?

Agreed, and there looks to be a TVS diode (SMCJ5.0A-TR, FUA) adjacent to it.

https://www.jameco.com/Jameco/Products/ProdDS/1395796.pdf