Reading warning signs and charging safely
LiPo cells communicate distress in fairly recognizable ways, and knowing them is a core robotics safety skill, not an optional extra. A swollen or 'puffy' LiPo pack, one where the pouch has visibly expanded from its original flat shape, is a sign that internal gas has built up from chemical breakdown inside the cell, usually from over-discharge, physical damage, age, or excessive heat. A swollen pack should be treated as compromised and taken out of service; continuing to charge or discharge it meaningfully raises the risk of the pack venting or catching fire. Physical damage, punctures, crushing, or a pack that's been dropped hard, carries the same warning: even if it looks fine externally, internal separator damage can create a short circuit that triggers thermal runaway with no further warning.
Safe charging practice follows directly from lithium chemistry's vulnerabilities. Chargers should always be set to match the pack's cell count and chemistry (a charger set for the wrong S count will overcharge and dangerously stress the cells), and packs should be charged on a fireproof surface or inside a LiPo charging bag, in case something does go wrong. Multi-cell packs should be charged with a balance charger, which monitors and equalizes each individual cell's voltage rather than just the pack's total voltage, because cells in a series pack can drift out of balance over time and a pack-level voltage reading can look fine even while one individual cell is dangerously overcharged. Unattended charging, especially overnight, is one of the most common causes of LiPo fires and is avoided by anyone who takes battery safety seriously.