Accordion is cool but I need only basic "collapse" functionality. => Panels keep opened, not auto collapsed, more panels can be opened at the same time.

Difference is only in specifying "data-parent" attribute. If it is specified it behaves as accordion, if not is simple collapse.
In actual version, it is on line 106:

'data-parent': '#' + parentId,

It would be nice to specify this in options. Something like

$( "#nav-tabs--fleet" ).tabCollapse( {
    accordion: true
} );

if(this.options.accordion){
    'data-parent': '#' + parentId,
}

It would be helpful.
Or there is some another workaround?