Hello, getting the error: “Pins of type Output and Power output are connected” even after I added the power flag to the schematic. I also checked all the GND and they are power input.
I see two fairly obvious possible causes:
- KiCad is right and you should not connect pin 13 to GND.
- There is an error in that symbol, and pin 13 should not be defined as an output.
This is ERC, not DRC, which applies to the PCB, changing the title
Yes, it’s Electrical ERC, not Design DRC. 
BTW, I know it can be a knee-jerk reaction to add a PWR_FLAG, but the situation where it’s usually applied is “Net has Power Input pin but no Power Output pin”. This one is different, it’s “Pins of type Output and Power Output are connected”.
Why adding the power flag (meaning additional power output is present on the net) should help?
This is (I guess, since you didn’t say) a BQ25505 or BQ25570 part:
VBAT_OK is indeed an output, so the symbol is correct and connecting it to ground is a mistake, as it will be short circuit if the IC tries to pull it high (actually the part has a 20k series resistor, so it won’t break anything, just waste a little energy for no reason). If you don’t need it, leave it unconnected.
You may or may not need a power flag on GND net because something may be driving it with a power output pin. You will know you need one if you also have ERC errors complaining of undriven power input pins on GND net. If you are delivering power via a power supply symbol (e.g. Battery) or a generic connector symbol with passive pins, or it is downstream of a filtering component with passive pins, then you need the flag to tell the ERC “this is a power net” (or it will complain that VSS is a power input not driven by a power output).
Your error here is connecting an output to a powered net, as this will mean the two can be “fighting” over it when the IC wants to drive high and that could be a smoke-releasing event for some circuits.
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