You’re at least the third person to say this without the disclaimer - only if the rubber flap was securely covering the ports when it was dropped in water.
You repeat this everywhere. The port requiring a flap has no bearing on the waterproofing of the battery which used an entirely separately gasket on the back cover.
You can clearly see here[0] that the gasket on the flap protects only the USB port from water ingress. The battery and sim are protected by the grey gasket on the rear cover.
The opening for the rear speakers in the back cover reinforces the fact that the flap is there to protect the interface of the USB port and its housing. The rear cover does not contact the USB port at all.
Making sure a rear cover has snapped into place is much less prone to failure than acquiring tools and applying heat to a glued on rear cover, de-soldering/disconnecting a battery and evenly re-applying and heating new glue.
