Well Honestly Dont Know The Actual Cause Behind That But In My Knowledge
The KZJ70/LJ70 Uses Two Batteries With 700 odd CCA Stock Battery Each.
This Gives Instant High Power Start On Even The Coldest Day.
One Battery Can Not Provide Enough Cranking Amps To Start The Diesel Engine (dependably)!
The Batteries Are Connected In "Parallel", Which Means That One Still Have The 12 Volts The Same As Everybody else!
Mostly Diesel Engine Needs High Crank to Start The Engine.
Bz Diesels Engines Are Notoriously Hard To Start When They're Cold
As With The Cold Weather Coming In Batteries Suffer Badly So 2 Will Work Best For That.
& Its Just Not This Toyota Model Which Uses 2 Batteries There Are Other Also ..