Can I charge lithium batteries in a series with lead-acid?

Charging Characteristics

When charging batteries in a series, the charging voltage is divided equally among the batteries. However, lithium batteries require a more complex charging profile to prevent overcharging and prolong their lifespan. Lead-acid batteries, on the other hand, can be charged with a simple voltage-limited charge controller. If you charge lithium batteries in series with lead-acid, the lead-acid batteries may be charged correctly, but the lithium batteries may be overcharged or undercharged, leading to reduced performance and lifespan.

Series Charging Risks

Charging lithium batteries in series with lead-acid can also cause electrical stress on the lithium batteries. Lithium batteries have a higher internal resistance than lead-acid batteries, which can lead to heat buildup during charging. If the lithium batteries are charged in series with lead-acid, the heat buildup can be even more pronounced, potentially causing damage to the lithium batteries.

Parallel Charging Solution

A safer and more efficient way to charge both types of batteries is to charge them in parallel. This allows you to use a single charge controller that can handle the combined capacity of both battery types. When charging in parallel, the charge controller will regulate the charging voltage and current to ensure that both batteries are charged safely and efficiently. This setup also provides redundancy, so if one battery type fails, the other can still provide power.