Why not using like super capacitors for buffering the current needed to spin the drive? Batteries can die..
Apart from that there are much better alternatives available. I recently bought three WD My Book 8 TB for 250 Euro each (should be around the same in Dollar) and they are smashing those Seagate SMR-Drives performance-wise and are even cheaper! Inside the case there are drives technically identical to HGST He8 but with reduced spindle speed of 5400 rpm. Also marketed as WD Red and WD Purple.
The drives use less power in idle and access because of the Helium and therefore they stay pretty cool and also very silent in idle. Performance is great, sequential transfer starting at ~193 MB/Sec. going down to like 95 MB/Sec. at the end. I have put all three of them in my Desktop and filled those empty My Book cases with old 2 TB Samsung 5400 rpm and Hitachi 7200 rpm drives i took out of my System after 6 years.
I guess i will never get warm with Seagate. The only Seagate drive i have is a external 2,5" USB3 HDD and its SMART Values (something with Calibration Retry Count) goes up like hell and the drive is clicking a lot in idle, even i didnt use it much at all.
Hitachi / HGST all the way for me, never failed me, exept those famous IBM / Hitachi "Deathstars DTLA-307030" with that very distinctive sound from Data-loosing-Hell.
Greetings from Germany
Thomas