Based on PWMtechnique, the energy from batterydischargesreturnto the mastertapeofDC, which has the advantagetransmittingenergy through two directions and realizes energy callback.
Each is, appropriately, adorned with a four-claw dragon on the battery cover, and the engraving process is rather lengthy: it involves 20 stages and takes four highly-skilled master craftsmen 36 hours, eight of which are dedicated just to the dragon's scales.