“The range isn’t enough, replacing the battery with lithium is too expensive, and sticking with lead‑acid leaves you short on distance…” This has become a common frustration for many electric‑vehicle owners. As a result, an “affordable” modification has gained popularity: adding a set of lithium batteries in parallel to the vehicle’s existing lead‑acid pack.

It sounds promising: lead‑acid batteries are stable and reliable, while lithium batteries are lightweight and efficient—why not combine the two for a perfect solution? Yet few realize that this seemingly smart pairing is quietly sowing safety risks.

When the “old workhorse” meets the “swift steed”: the innate incompatibility of two types of batteries

Imagine that lead-acid batteries are like hardworking old oxen—dutiful and reliable, yet only moderately efficient—while lithium batteries are pedigreed racehorses: superb in performance, but with a fiery temperament.

They are, in fact, two entirely different “organisms”:

Operating voltage differences: When fully charged, the voltage of a lead-acid battery is approximately 12.6-12.8V , whereas lithium batteries have reached 12.8-13.2V This tiny voltage difference generates a massive inrush current at the moment of parallel connection—much like a high water level crashing violently into a low one.

Different internal resistance characteristics: Lithium batteries have a much lower internal resistance than lead-acid batteries. This means that during discharge, lithium batteries tend to “take on too much work,” making them prone to damage from over‑discharge; and during charging, they “consume more energy,” increasing the risk of overcharging.

Mismatched life cycles: Lead-acid batteries typically can be charged and discharged. 300-500 Next, while lithium batteries can reach 1000 and above. This asynchronous aging process causes the entire system to become increasingly unstable.

The Lifesaving Switch: The Critical Role of the Circuit Breaker

It is precisely under such complex circumstances that the air switch—often referred to as an “air breaker”—has evolved from an ordinary electrical component into a life-saving device.

It is not merely a switch; it is also a guardian of the triune essence:

1 , the “traffic cop” of electric current

Before connecting two batteries in parallel, a circuit breaker ensures that each battery first reaches a similar voltage level, thereby preventing destructive inrush currents that could occur with a direct connection.

2 , the “emergency brake” on risk

When the system malfunctions—such as a battery overheating or a sudden surge in current—the circuit breaker can quickly disconnect the circuit, preventing the fault from escalating. This response time can be as short as tens of milliseconds.

3 , the “security isolation” of maintenance

Professional advice: If you absolutely must mix batteries,

Although we strongly advise against mixing batteries on your own, if you do have a specific need, please at least follow these guidelines:

Essential safety measures:

Each battery circuit is equipped with a dedicated circuit breaker—choose models with an appropriate rated current and strong breaking capacity.

Use a dedicated battery isolator—intelligently manages the charge and discharge process.

Regularly inspect the connection status—including line temperature, loose connection points, and other factors.

A safer choice:

Consider using DC-DC The converter provides complete isolation between the two battery types, or you can directly select a single‑type battery system that matches your requirements.

Today, as electric vehicles have become an everyday means of transportation, battery safety is directly linked to the personal and property security of vehicle owners. In this seemingly simple modification, the circuit breaker plays an irreplaceable role as a guardian of safety.

Remember: Any attempt to skip critical safety components is a shortcut at the expense of lives. When balancing range and cost, never compromise on safety.