There is no magic bullet but persistence, and even that will fail if the PB is unserviceable.

Check the AC adapter, for output voltage and temperature, after 5min and 1hr. Is it warm or ridiculously hot? Is the battery warm or, again, ridiculously hot after the same intervals. 30% of full charge is vastly insufficient as a working charge.

Be prepared to reset the PMU ten times, if that is what it takes. If AC adapter and battery check out as at least adequate, and reset of the PMU does nothing for you, an inside job is in order, starting from de-fluff and de-dust, and proceeding by way of minute inspection, of ensuring the presence and integrity of all sub-boards and units, of reseating all connectors and verifying the integrity of all cables. Specifically, measure the voltage of the internal backup battery.

Then reassemble, and allow the PB to stay on charge for 24hr. If the battery and AC adapter are adequate to reach full battery voltage, leave the whole on charge for another 24hr to get the backup battery charged. Then reset the PMU again, and rebegin the process,

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