iPhone 6S battery drain - 0.02A draw before prompt to boot

So, I have a working iPhone 6S, boots normally, charges normally, everything works but it discharges the battery faster than normal. Even when the phone is not powered on something is draining the battery and after like a day battery is dead.

First, I thought it’s a tristar issue and I replaced it with a new one, but the problem is not solved. Then I thought that maybe the battery is bad so I replaced it with a new one, but problem is still present.

When I connect the board on DCPS I get 0.02A draw before prompt to boot. I have checked PP_1V8_ALWAYS and I get 1.8V, I also checked PP_BAT_VCC and I get battery voltage, so I guess these lines are OK?

I have also probed around tristar and tigris and I didn’t find anything wrong, no shorted caps. I also did diode mode measurements on all connectors and all readings are OK.

What can I try more, what could be a problem?