def lip2en(BM, perc_lipid):
    """Percent lipid composition to percent energy stores

    Args
    ----
    BM: float or ndarray
        Body mass of animal
    perc_lipid: float or ndarray
        Percent lipids of animal's body composition

    Returns
    -------
    en: float or ndarray
        Total energy stores

    """
    PTBW = 71.4966 - 0.6802721 * perc_lipid
    return 40.8 * BM - 48.5 * (0.01 * PTBW * BM) - 0.4
