Can I Combine Flooded Lead-Acid with Lithium Batteries?

Incompatible Chemistry

Combining flooded lead-acid (FLA) batteries with lithium-ion (Li-ion) batteries is not feasible due to their fundamentally different chemistries. FLA batteries operate at 12V, 6V, or 2V, with a maximum depth of discharge (DOD) of 50% to prevent sulfation. Li-ion batteries, on the other hand, operate at 12V, with a maximum DOD of 80% to 90%. Mixing these two types can lead to over-discharge, thermal runaway, or electrical shorts.

Electrical Compatibility

The electrical characteristics of FLA and Li-ion batteries also pose a challenge. FLA batteries have a higher internal resistance, which can cause voltage drops and heat buildup when charging or discharging in parallel with Li-ion batteries. Furthermore, the charging profiles of the two battery types differ significantly, which can lead to overcharging or undercharging if not properly managed. A mismatched charging profile can cause damage to either battery type or both.

Safety Risks and Damage Prevention

To prevent damage to the lithium batteries, it is essential to disconnect them from the FLA batteries when the system is not in use or when the FLA batteries are being charged or discharged. This can be achieved through a battery management system (BMS) or a separate charging circuit. A BMS can monitor the state of charge, voltage, and current of both battery types and disconnect the lithium batteries if they become overcharged or over-discharged.