Abstract: A compact heat battery (CHB) may comprise a casing, a tube containment sheath, a bundle of hermetically sealed phase change material (PCM) encapsulation tubes, and encapsulation tube inserts. An insulation envelope and insulation shield may be positioned radially outward from the casing. As an alternative the casing, insulation, and insulation shield can be integrated into a double-walled vacuum cylinder. The cylindrical containment sheath can open and close along a split-seam in response to radial expansion of the tubes. The natural packing of the encapsulation tubes within the containment sheath can distribute a heat transfer fluid through the interstitial spaces between the encapsulation tubes. Floating baffle plates provide for axial containment and expansion of the encapsulation tube bundle. The CHB of the present invention can allow for increased tube density, providing increased heat absorption and decreased CHB dimensions.