Humidity sounds harmless—but for lithium-ion batteries, it's a slow, silent killer.

Humidity accelerates corrosion¹, degrades electrolyte stability², causes swelling, and compromises battery performance³ and safety over time.

If your devices are used or stored in humid environments⁴, battery failure⁵ could be just a matter of time. Here's what I’ve learned about protecting them⁶.

What happens when moisture gets inside lithium-ion batteries?

Tiny amounts of water can do serious damage—without any visible signs.

Moisture reacts with battery chemicals, creating corrosive compounds like hydrofluoric acid that degrade internal parts and reduce battery lifespan.

Let’s break it down

Here’s what typically happens:

• Electrolyte hydrolysis⁷: Water reacts with lithium salt (e.g. LiPF₆), producing HF acid
• HF acid attack⁸: Corrodes electrodes, separators, and even casings
• Increased resistance⁹: Ions move less efficiently, causing performance drops
• Gas formation: Trapped moisture causes internal swelling over time

In one project, we had a batch of wearable devices¹⁰ returned from Southeast Asia—all with swollen batteries¹¹. Lab analysis showed high internal moisture content, even though the cells were factory-sealed. Turns out, the plastic enclosures were slightly permeable, and we didn’t account for tropical humidity¹².

How does high humidity impact battery performance?

Even without a visible leak, moisture changes everything inside the battery.

High humidity reduces energy efficiency, lowers cycle life, and increases internal resistance—leading to shorter runtime and faster aging.

Performance effects at a glance:

Humidity Level	Impact on Battery	Notes
<30% RH	Risk of dry-out, static buildup	May affect shelf life
40–60% RH	Safe zone for most devices	Ideal for storage
>70% RH	Moisture ingress likely	Requires barrier protection
>90% RH	High risk of electrolyte breakdown	Rapid degradation

In my lab tests, we stored two identical battery-powered sensors¹³—one at 45% RH, the other at 85% RH. After six months, the high-humidity unit¹⁴ had 18% lower capacity and 25% higher internal resistance¹⁵. That’s without any visible corrosion.

What safety issues can humidity cause?

Corroded cells don’t just perform worse—they get dangerous.

Humidity increases the risk of short circuits, swelling, leakage, and thermal runaway—especially if batteries are used near their limits.

Here’s what can go wrong:

1. Swelling

Moisture reacts with battery chemicals, forming gas → pouch cell balloons → pressure builds.

2. Leaking

Degraded seals or casing corrosion allows electrolyte to seep out—highly flammable and toxic.

3. Fire hazard

If moisture-induced corrosion causes an internal short, you may get a chain reaction: heat, thermal runaway, and fire.

I once dealt with a smartwatch recall where a few units literally “puffed up” after being worn during workouts. Root cause? Sweat humidity penetrated the gasket over time, causing internal swelling.

How can we protect lithium batteries from humidity?

Good design choices early on can save you from big problems later.

Use hermetic sealing, low-permeability materials, desiccants, and humidity testing to prevent moisture damage.

Practical strategies:

• Seal the pack: Ultrasonic welding or epoxy-sealed pouches prevent ingress
• Desiccant bags¹⁶: Especially for packaging or long-term storage
• Barrier films: Low-permeability plastics like PVDC or aluminum-laminated layers
• Humidity chamber testing¹⁷: Expose sample units to 85% RH @ 60°C to simulate worst-case

In one wearable project, we added just one silica desiccant sachet inside the final box—battery life at shipment went from 6 months to 14 months with no capacity loss. Cheap fix, huge result.

Conclusion

Moisture is invisible—but its damage isn’t. For small lithium-ion batteries, humidity control means longer life, better performance, and safer products.