Parts you write, see and print.

// batteries.hcad: a holder for AA cells
import std;

@param immutable cells = 4;
immutable aa = 14.5.mm, play = 0.4.mm;
immutable hole = aa + play, pitch = hole + 2.mm;

@part
Solid holder()
{
    auto b = box(cells * pitch + 2.mm,
            pitch + 2.mm, 22.mm)
        .fillet(edges.parallel(Z), r: 3.mm);

    // a pocket for each cell, its rim chamfered
    foreach (i; 0 .. cells)
        b -= cylinder(d: hole, h: 22.mm)
            .move(x: (i - (cells - 1) / 2.0) * pitch,
                z: 3.mm);
    b = b.chamfer(edges.of(faces.top), d: 0.6.mm);

    // a grip on both long sides, last
    return b
        .knurl(faces.front, kind: "diagonal",
            pitch: 3.mm)
        .knurl(faces.back, kind: "diagonal",
            pitch: 3.mm);
}

// a cell in the first pocket, to see it fit
@part("Yellow Pop", alpha: 0.4, export: false)
Solid cell()
{
    auto body = cylinder(d: aa, h: 49.5.mm);
    auto tip = cylinder(d: 5.5.mm, h: 1.mm)
        .move(z: 49.5.mm);
    return (body + tip)
        .move(x: -(cells - 1) / 2.0 * pitch, z: 3.mm);
}

unittest
{
    assert(hole > aa, "an AA cell does not fit");
    assert((holder & cell).volume < 0.01.mm ^^ 3,
        "the cell rubs against the holder");
}