They’re compact, powerful, and everywhere—but can they survive the deep?

Yes, small lithium-ion batteries¹ can be used in underwater devices—but only with proper sealing², thermal protection³, and pressure resistance.

Many people think lithium batteries⁴ and water are a dangerous mix—and they can be. But with the right design, they power everything from underwater drones⁵ to subsea sensors⁶. Let’s dive into how.

What makes lithium-ion batteries suitable for underwater use?

They offer lightweight power—but only if you can keep them dry.

Their high energy density⁷ and long cycle life⁸ make them ideal for underwater use, as long as they're properly sealed and isolated from water⁹.

Why we choose lithium over other chemistries

Energy-to-weight ratio matters

Battery Type	Energy Density (Wh/kg)	Recharge Cycles	Typical Use Case
Lithium-ion10	150–250	500–2000	Underwater drones, ROVs
NiMH11	60–120	300–500	Older equipment
Lead-acid12	30–50	100–300	Buoys, stationary sensors

Lithium-ion¹³ stands out for deep-sea use, where space and weight are limited. I’ve personally used 18650 cells¹⁴ in a tethered camera module¹⁵ that needed to stay light, neutral in buoyancy, and run 3+ hours continuously—only lithium could deliver that.

What are the biggest risks of using lithium-ion batteries underwater?

Water and lithium don’t mix—unless you separate them properly.

The biggest risks are water ingress, pressure deformation, and thermal instability—each of which can damage the battery or cause a short.

Main threats explained

1. Water ingress

• Even a tiny leak can short the cell
• Saltwater accelerates corrosion and chemical reactions

2. Pressure damage

• Deep water = high pressure = casing deformation
• Weak spots can lead to cracks or swelling

3. Temperature shifts

• Cold water lowers capacity and efficiency
• Warm climates may risk overheating in sealed pods

One time, I tested a device at 50m depth. It worked fine—until we forgot to vent the battery pod before surfacing. Pressure differential cracked the case, letting saltwater seep in during ascent. The battery fizzled out within seconds.

How do we protect lithium-ion batteries for underwater use?

It’s all about isolation, insulation, and intelligent design.

Encapsulation, potting, double-hull systems, and thermal regulation are key techniques to make lithium batteries safe for underwater use.

Common protection methods

Potting

• Encases battery in epoxy or gel
• Ideal for small or disposable devices

Pressure-rated housings

• Custom-made aluminum or polycarbonate pods
• Handles depths of 100–1000m or more

Desiccants and venting

• Silica gel prevents humidity buildup
• Gore vents equalize pressure without letting water in

Smart battery management systems (BMS)

• Monitors temperature, current, and voltage
• Shuts down if instability is detected

In my latest project, we used vacuum potting to fully encapsulate a 3S lithium pack, sealed it in a pressure-rated polycarbonate shell, and added a thermal sensor. That unit has been submerged for over 18 months—still going strong.

Which underwater devices use lithium-ion batteries?

If it swims, dives, or floats—it probably uses lithium-ion.

Lithium-ion batteries are used in underwater drones, buoys, GPS trackers, subsea cameras, and autonomous sensors.

Real-world examples

Device Type	Battery Role	Runtime
ROV (drone)	Powers thrusters and control boards	2–6 hours
Subsea sensor pod	Runs data loggers, acoustic modems	Up to 1 year
Smart buoy	GPS + signal + solar recharging	24/7 uptime
Autonomous camera	Image capture, data buffer, flash memory	3–12 hours

I’ve personally worked on an underwater inspection ROV¹⁶ that uses two lithium-ion packs¹⁷ (14.8V, 10Ah each), running in parallel. They’re packed in aluminum tubes with O-ring seals and nitrogen purge—battery checks every dive, and zero failures after 30+ deployments.

What should we consider before designing an underwater battery system?

Plan for pressure, plan for leaks, and always assume the worst.

Depth rating, thermal behavior, weight balance, charging method, and battery monitoring are critical design elements for underwater battery systems.

Key design points

• Depth rating: Always overengineer the case by 2–3× expected pressure
• Charge isolation: Never recharge batteries while they're wet
• Thermal sensors: Critical for sealed environments
• Neutral buoyancy: Balance battery mass with foam or ballast
• Fail-safe BMS: Detect early failures or pressure-triggered disconnects

In one test, I installed a low-pressure switch that triggered when water ingress began to deform the inner shell. The BMS instantly cut off power—saving the rest of the system from a cascade failure.

Conclusion

Yes, small lithium-ion batteries can be used underwater—if you isolate them, protect them, and respect the ocean’s power.