With a lead acid battery, an external voltage sensing relay can be used to prevent over discharge, and shed any non critical loads. Lithium batteries can be destroyed if allowed to completely discharge, and can result in cell shorts/fire/failure during subsequent recharge. The next difference is that lead acid batteries, while they can be degraded by discharging to empty, will recover, and continue to safely operate. So if a single cell exceeds the max safe voltage, the electrolyte decomposes, causing swelling, possible venting, and internal shorts/fire. Lithium cells do not self limit their voltage during absorb. So balancing is needed, and a BMS can perform this. The major difference is that a lead acid battery can self balance its cells during absorb through the shuttle reactions.
