I have large battery on left side of trunk, smaller on right.
Last week, car would not start.
Found left (larger) low on voltage, right was fine.
When calling for replacement battery quotes, was told 'primary' is the right/smaller one; assume their system is wrong, since left was low, and likely causing the no start.
a) which is the primary battery (left/right, large/small)?
b) with (assumed) primary battery low/drained, by did secondary battery not 'jump in'?