Ground Vehicles: Don’t Get Mixed Up with Batteries

BLUF: It’s not recommended to mix old and new batteries in vehicles that require multiple batteries.

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Maintenance leaders, it's generally recommended to use new lead acid batteries of the same NSN in vehicles that require multiple batteries. And, if you need to replace batteries, it's advisable to replace all of them at the same time. Why’s that?

Here’s some reasons why it’s not good practice to mix old batteries with new batteries in vehicles or equipment that require multiple batteries:

Voltage Difference - batteries gradually lose their charge over time. When you mix a new battery with an old one, there can be a significant difference in their voltage levels. This can lead to inconsistent performance or unreliable operation of the device. The weaker battery may discharge faster and reduce the overall battery life.
Imbalanced Discharge - mixing new and old batteries can result in imbalanced discharge rates. The weaker battery may struggle to keep up with the power demands of the vehicle, causing it to drain faster or fail to deliver sufficient power. This can result in reduced performance or unexpected power shortage for engine startup.
Battery Leakage - old batteries, particularly those nearing the end of their lifespan, are more prone to leakage. When a leaking battery contacts other batteries, it can cause corrosion or damage to the surrounding components. Mixing a leaking battery with a new one can potentially damage the vehicle. It can also pose safety hazards.
Battery Management Difficulty - it becomes challenging to keep track of their individual performance and lifespan. It's important to know when to replace batteries to ensure optimal performance and prevent potential issues. Mixing batteries complicates this process, as you may have to monitor and replace them separately.

You’ll also want to check out Tactical Vehicles: Shocking Truth behind Defective Batteries.

Editor’s note: A thanks to Dr. Yi Ding of DEVCOM GVSC for his contribution to this article.