<p>The increasing demand for electric bikes necessitates advancements in battery thermal management (BTM) to ensure battery packs' performance, safety, and longevity. Phase change material (PCM)-based thermal management is known for effectively controlling the temperature of lithium-ion batteries (LIB) and keeping excellent temperature uniformity. However, their performance is sensitive to melting point, latent heat, and surrounding temperature. This transient numerical study examines the effect of surrounding temperature (<i>T</i>_<i>o</i>), ranging from 15 °C to 45 °C, on the thermal performance of a PCM heat sink integrated with convective surface cooling built on a battery pack made of LIBs. Natural convection (NC) has been observed to effectively keep the maximum temperatures (<i>T</i>_max) below the optimal limit of 40°C across all the studied <i>T</i>_<i>o</i> values. Forced convection (FC) surpasses this threshold when the <i>T</i>_<i>o</i> exceeds 42 °C. The maximum temperature difference across the pack, "Δ<i>T</i>_max," increases when <i>T</i>_<i>o</i> decreases. NC provides a superior temperature uniformity at all the assessed surrounding temperatures, but FC does not sustain the uniformity when <i>T</i>_<i>o</i> is below 26 °C. The key findings include determining the critical temperature thresholds of melting of the PCM and the proposed cooling strategy for optimizing the PCM-based BTM.</p>