High-Temperature Battery ER18505S: How the 3.6V LiSOCl₂ Cell Powers Oil Drilling, Autoclaves and Extreme IoT Sensors
High-Temperature Battery ER18505S: How the 3.6V LiSOCl₂ Cell Powers Oil Drilling, Autoclaves and Extreme IoT Sensors
Published by SER GROUP LIMITED / Guangzhou Serui Battery Technology Co., Ltd. — www.serui-battery.com
Introduction
Engineers who design for extreme environments share a quiet frustration: almost every off-the-shelf battery is engineered for a 25 °C room. Push it to 85 °C and the electrolyte dries out. Push it to 125 °C and the separator melts. Push it to 150 °C — inside a downhole drilling tool, an autoclave cycle, or a desert data logger — and the cell leaks, vents or simply goes silent in the field.
For more than four decades, the chemistry that has solved this problem is LiSOCl₂ battery (lithium thionyl chloride), and within that family the ER18505S has become the reference cell for applications that must survive both arctic cold and furnace-grade heat. Rated from −30 °C to +150 °C, delivering 3.6 V and 3.2 Ah in a compact 18 × 50.5 mm cylindrical can, the ER18505S is a true high-temperature battery built for oil downhole tools, medical sterilisation cabinets, pipeline inspection gauges (PIGs), mine exploration probes and GPS trackers that live inside shipping containers parked in the sun.
This article walks through why LiSOCl₂ chemistry dominates high-temperature primary power, what the "S" suffix in ER18505S actually means, the engineering specs that make the cell safe at 150 °C, and the real-world use cases where design teams at www.serui-battery.com have deployed it. If you are qualifying a power source for a downhole, autoclave or desert-sensor application, by the end you will know exactly what to ask your supplier.
What Is a High-Temperature Battery — and Why Do Standard Cells Fail at 85 °C?
1.1 The definition
A high-temperature battery is a primary or secondary cell designed to deliver its rated capacity continuously at ambient temperatures above the conventional industrial limit of +60 °C. In practice, the market splits these cells into three tiers:
Extended-temperature cells (+85 °C) — used under automotive hoods, in desert outdoor enclosures and inside sealed IoT housings that bake in the sun.
High-temperature cells (+125 °C) — used in industrial gauges, underground mining instruments and well-logging tools that sit a few hours at a time in hot holes.
Extreme / ultra-high-temperature cells (+150 °C and above) — used in MWD (Measure While Drilling) tools, permanent downhole gauges, industrial autoclaves and sterilisation cycles.
The ER18505S sits in the third tier: it is specified for continuous operation from −30 °C up to +150 °C, with short-duration exposure to even higher temperatures during a drilling run or sterilisation cycle.
1.2 Why ordinary batteries fall apart in heat
A standard lithium-ion, Li-MnO₂ or alkaline cell relies on three things that heat destroys:
A polymer separator that melts or shrinks above 80–100 °C, causing internal short circuits.
An organic electrolyte whose vapour pressure rises rapidly, swelling the can and eventually venting through the safety valve.
A passivation layer that, at moderate temperature, protects the lithium anode — but at high temperature either dissolves too slowly (causing voltage delay) or too fast (accelerating self-discharge).
LiSOCl₂ chemistry is the rare system in which the electrolyte itself (thionyl chloride, SOCl₂) is thermally stable well above 150 °C, and in which the separator and anode design can be engineered to survive continuous heat. This is why the ER18505S — not a Li-ion 18650 or a standard Li-MnO₂ AA — is the cell of choice inside a 150 °C downhole tool.
1.3 The cost of a cell failure in the field
In a consumer device, a dead battery is an inconvenience. In a downhole MWD tool, it is a fishing job: pulling several thousand metres of drill string to replace a cell costs an oil operator USD 50,000–250,000 per day. In an autoclave, a leaked cell contaminates a batch of surgical instruments. In a pipeline PIG, a dead battery means a lost tool worth hundreds of thousands of dollars stuck in a 100 km gas line. The economic case for a properly specified high-temperature LiSOCl₂ battery is overwhelming — which is why operators specify the ER18505S rather than substitute a cheaper cell.
LiSOCl₂ Battery Chemistry: Why It Survives 150 °C
2.1 The core reaction
A LiSOCl₂ cell uses a lithium metal anode, a porous carbon cathode and a non-aqueous electrolyte consisting of thionyl chloride (SOCl₂) with dissolved lithium tetrachloroaluminate (LiAlCl₄). The overall discharge reaction is:
4 Li + 2 SOCl₂ → 4 LiCl + S + SO₂
In plain English: the lithium anode oxidises, thionyl chloride is reduced at the carbon cathode, and the solid products (lithium chloride and sulphur) plus dissolved sulphur dioxide remain trapped inside the can. This chemistry has several properties that make it the natural choice for extreme temperature:
Very high nominal voltage (3.6 V) — almost double the 1.5 V of alkaline and 0.6 V higher than Li-MnO₂. One cell replaces two alkaline cells in series, saving space and cost.
Very high energy density — the ER18505S delivers 3.2 Ah at 3.6 V ≈ 11.5 Wh in a 19 g 2/3-A-size can, an energy density above 600 Wh/L.
Extremely low self-discharge — under 1% per year at room temperature, enabling a 10-year storage life.
Inherent thermal stability — thionyl chloride boils at 79 °C but does not decompose explosively at 150 °C under normal discharge; the cell is hermetically crimped and vented with a pressure-relief mechanism.
2.2 The passivation trade-off
One quirk of LiSOCl₂ chemistry is passivation: on first exposure to air, the lithium anode forms a thin LiCl film that prevents further corrosion. This is good for shelf life (hence the 10-year storage) but creates a short voltage delay when the cell is first put under load — the terminal voltage dips before the film breaks down.
In a standard-temperature ER18505, this delay is mild. In the high-temperature ER18505S, SER engineers use a modified anode formulation and electrolyte concentration to:
Minimise voltage delay even after years of storage.
Maintain stable pulse performance at 150 °C, where the passivation layer would otherwise break down too quickly and accelerate self-discharge.
This is exactly what the "S" suffix denotes: the high-temperature / super variant of the ER18505 platform, reformulated for +150 °C operation.
2.3 LiSOCl₂ vs. competing chemistries at high temperature
Chemistry | Nominal voltage | Max continuous temp | Shelf life | Typical high-temp application |
Li-SOCl₂ (ER18505S) | 3.6 V | +150 °C | 10+ years | Downhole MWD, autoclaves, PIGs |
Li-SOCl₂ (standard ER18505) | 3.6 V | +85 °C | 10 years | Smart meters, security, generic IoT |
Li-MnO₂ (ER18505 / CR AA) | 3.0 V | +60–70 °C | 5–10 years | RFID, backup, consumer medical |
Li-FeS₂ (L91 / FR AA) | 1.5 V | +60 °C | 10 years | Alkaline replacement |
Li-ion 18650 | 3.6–3.7 V | +60 °C (de-rated) | 2–3 years | High-drain consumer tools |
For continuous operation above 85 °C, LiSOCl₂ is the only mature primary chemistry in mass production — which is why the ER18505S has no real competitor in its temperature class.
Product Deep Dive: ER18505S 3.6V 3.2Ah High-Temperature LiSOCl₂ Cell
3.1 Specifications
The ER18505S is SER's flagship high-temperature 2/3-A-size cylindrical LiSOCl₂ cell, purpose-built for downhole, sterilisation and extreme-environment sensing.
Parameter | ER18505S specification |
Chemistry | Lithium thionyl chloride (Li-SOCl₂), primary |
Model suffix | S = high-temperature grade (up to +150 °C) |
Nominal voltage | 3.6 V |
Open-circuit voltage | ≥ 3.64 V (fresh cell, 23 °C) |
Nominal capacity | 3,200 mAh (3.2 Ah) @ 100 mA to 2.0 V, 23 °C |
Maximum continuous current | 1,000 mA (high-temp grade, de-rated at 150 °C) |
Maximum pulse current | 2,000 mA (short pulses, e.g. telemetry bursts) |
Dimensions | 18 mm diameter × 50.5 mm height (2/3 A form factor) |
Operating temperature | −30 °C to +150 °C |
Storage temperature | Clean, dry, ≤ +20 °C ventilated |
Storage life | 10 years (at ≤ 20 °C) |
Termination options | S standard, T solder tabs, P axial pins; special terminations on request |
Branding | SER or OEM private label |
Certifications | CE, UL, SGS, IEC, UN38.3, RoHS, ISO 9001 factory |
3.2 Why 18 × 50.5 mm is the sweet spot
The 2/3-A footprint (18505 in IEC naming: 18 mm diameter, 50.5 mm length) is one of the most widely adopted cell sizes in industrial primary batteries. It fits:
Standard AA/2/3-A battery holders, reducing custom mechanical design.
Downhole tool battery sleeves that are already qualified across the industry.
PIG (pipeline inspection gauge) battery modules, where cylindrical cells are stacked in series-parallel strings to reach 12 V or 24 V.
The ER18505S drops directly into many existing battery packs that were originally designed for standard-temperature ER18505 cells — but now survive the higher temperatures of deeper wells and hotter sterilisation cycles.
3.3 Continuous vs. pulse current
The cell's 1,000 mA continuous and 2,000 mA pulse ratings are deliberately generous. A typical downhole telemetry module draws:
100–300 mA while logging sensors continuously.
1,000–2,000 mA for a 2–10 second mud-pulse or electromagnetic telemetry burst.
The ER18505S handles both without a supercapacitor reservoir, simplifying pack design. For applications that need even higher pulses (e.g. GSM modules in desert trackers), SER recommends pairing the cell with a small tantalum or EDLC capacitor — a standard design-in service our engineering team provides.
3.4 The 150 °C rating, honestly
A common trick in the high-temperature battery market is to quote "survival" temperature (the cell does not explode) rather than "operation" temperature (the cell delivers capacity). The ER18505S is rated for operation at 150 °C, not just survival. At 150 °C, expect:
Capacity to de-rate to roughly 60–70% of the 23 °C nameplate (i.e. ~2.0–2.2 Ah usable).
Self-discharge to accelerate to 5–10% per month at 150 °C — which is fine for a tool that spends hours or days in the hole, not years.
Voltage delay to become negligible (the passivation layer dissolves quickly at high temperature).
Engineering teams sizing a 150 °C tool should de-rate accordingly; our application engineers routinely help customers size strings for specific run times.
From −30 °C to +150 °C: What That Temperature Range Actually Means
A 180-degree span between minimum and maximum operating temperature is not marketing — it is a deliberate response to where industrial sensors live.
4.1 Cold-side performance (−30 °C)
At −30 °C, most alkaline cells deliver less than 30% of their nameplate capacity, and Li-ion cells slow to a crawl. The ER18505S, by contrast, retains >80% of rated capacity at −30 °C at moderate drain rates. This matters for:
Arctic oil and gas operations.
Alpine weather stations and avalanche sensors.
Refrigerated cold-chain loggers that ride inside containers at −25 °C.
4.2 Hot-side performance (+150 °C)
On the hot side, 150 °C is the temperature reached by:
Bottom-hole assemblies in deep onshore wells (reservoir temperature often 125–175 °C).
Industrial autoclaves running at 134 °C for 30–60 minute sterilisation cycles.
Pipeline PIGs moving through hot crude.
Black-box data loggers attached to engines or exhaust systems.
A cell that can run at both extremes — and survive thermal cycling between them — eliminates the need for two different battery designs and two qualification programmes.
Real-World Applications of the ER18505S High-Temperature LiSOCl₂ Cell
5.1 Oil & gas: downhole MWD and logging tools
This is the killer application for the ER18505S. Measure-While-Drilling (MWD) tools, Logging-While-Drilling (LWD) tools and permanent downhole gauges are bolted directly above the drill bit. They spend hours to days at bottom-hole temperatures of 125–175 °C, logging pressure, temperature, gamma ray and azimuth, then transmitting data to the surface via mud-pulse telemetry.
Standard-temperature cells fail here within minutes. The ER18505S, stacked in custom series-parallel packs inside pressure-compensated oil-filled sleeves, is the power source that makes a multi-day drilling run possible. The 2,000 mA pulse rating directly drives the telemetry transmitter.
5.2 High-temperature sterilisation cabinets and autoclaves
Medical autoclaves and industrial sterilisation cycles run at 121–134 °C for 20–60 minutes. Data loggers that ride inside the load to verify temperature uniformity must survive dozens to hundreds of these cycles. A standard battery leaks or dries out after a handful of cycles; the high-temperature ER18505S powers the logger through hundreds of cycles over a multi-year service life.
This is also why the cell is sometimes called an "autoclave battery" or "sterilisation battery" in medical-equipment catalogues.
5.3 Pipeline inspection gauges (PIGs)
Smart PIGs that inspect oil and gas pipelines travel at 2–5 m/s inside the line, logging metal loss, curvature and geometry over hundreds of kilometres. They experience hot crude (up to 80–120 °C), high pressure and vibration. The ER18505S is stacked in packs of 10–20 cells to provide the 12 V / 24 V rail and the multi-month energy budget a PIG needs.
5.4 Mine exploration and geophysical probes
Downhole mining probes, borehole seismic sensors and geothermal exploration instruments are lowered into boreholes where temperatures climb steadily with depth. The ER18505S's −30 to +150 °C range covers both surface winter conditions and deep-hole heat.
5.5 GPS trackers and asset loggers in hot environments
Container GPS trackers bolted to intermodal shipping containers see internal temperatures of 70–85 °C on a sun-baked container deck. A standard Li-SOCl₂ cell de-rates quickly in that heat; the ER18505S maintains its 10-year design life and delivers the 1,000–2,000 mA pulse needed for GPS acquisition and GSM transmission.
5.6 Aerospace, defence and industrial backup
The cell is also used in:
Aircraft emergency locator transmitters (ELTs) that must survive cockpit bay temperatures.
Military and ground-support equipment operating in desert environments.
Real-time clock (RTC) and SRAM backup memory in industrial PLCs mounted near furnaces.
Solar-powered data loggers in desert weather stations, where the enclosure itself reaches 70 °C.
Design-In Considerations for the ER18505S
6.1 De-rate for temperature
Treat the 3.2 Ah nameplate as a 23 °C figure. At 125 °C continuous, plan for ~50–60% usable capacity; at 150 °C, plan for ~60–70% for short-duration runs.
6.2 Manage voltage delay after long storage
If the cell has been stored for more than 12 months, expect a brief voltage dip on first load. Mitigate this with a 1 kΩ pre-load for a few seconds, or by specifying a low-passivation anode option at the time of order.
6.3 Series-parallel strings need balancing
When cells are stacked to reach 12 V, 24 V or higher, specify matched-capacity and matched-voltage grades. SER provides sorting on request for pack integrators.
6.4 Termination and mechanical design
Choose the termination at the BOM stage: standard snap (S) for holders, solder tabs (T) for welded packs, axial pins (P) for PCB-mount modules. Swapping after qualification wastes weeks.
6.5 Shipping and transport
LiSOCl₂ cells are classified as UN 38.3 Class 9 dangerous goods. SER ships every batch with the UN38.3 test summary, MSDS and ADR/IATA paperwork so your forwarder can move them by air or sea without delay.
6.6 Worked example: sizing a downhole pack
To make the de-rating numbers concrete, consider a typical MWD tool that draws 150 mA continuously while logging sensors and needs a 1.5 A, 6-second telemetry pulse every 30 seconds.
Average current = 150 mA + (1.5 A × 6 s / 30 s) = 150 mA + 300 mA = 450 mA.
At 150 °C, the ER18505S delivers ~65% of 3,200 mAh ≈ 2,080 mAh usable.
Run time per cell = 2,080 mAh / 450 mA ≈ 4.6 hours.
For a 20-hour drilling run, stack 5 cells in parallel (to maintain 3.6 V rail and multiply capacity) — giving ~23 hours of reserve.
If the tool needs a 12 V rail for the telemetry transmitter, stack 3 such groups in series (3 groups × 3.6 V = 10.8 V, close enough with a boost).
This is exactly the kind of back-of-envelope calculation our application engineers run with customers during the first design-in call.
6.7 Frequently asked questions
Q: Can I substitute a standard ER18505 (non-S version) for my 125 °C application? A: Technically it will not vent, but its capacity at 125 °C collapses to ~30%, and self-discharge accelerates sharply. The S-grade is reformulated for high-temperature operation; the cost difference is trivial compared with a failed run.
Q: Is the ER18505S rechargeable? A: No. It is a primary lithium cell. Recharging causes venting, leakage and safety risk. For rechargeable high-temperature applications, LiFePO₄ packs are the usual alternative but they cannot reach 150 °C continuously.
Q: How is the cell shipped? A: Fresh cells are shipped at ~30% state of discharge (open-circuit voltage 3.64 V+) with insulation resistance tested. They are classified UN38.3 Class 9 dangerous goods; all paperwork accompanies the shipment.
Q: What is the typical lead time? A: Standard ER18505S stock ships within 5 working days. Custom packs, solder tabs or private-label printing add 2–3 weeks for pilot runs and 4–6 weeks for volume.
Why Source the ER18505S from SER?
7.1 Who we are
SER GROUP LIMITED and its manufacturing arm, Guangzhou Serui Battery Technology Co., Ltd., has specialised in primary lithium batteries since 2004. We operate three production bases, 16 advanced manufacturing lines, and more than 1,650 staff, with a monthly output of 20 million primary cells and 600,000 battery packs. Our product line spans:
Li-SOCl₂ cylindrical cells — including the ER18505 / ER18505S high-temperature, ER14505, ER26500, ER34615 and high-temperature variants.
Li-MnO₂ cylindrical and pouch cells — the CR-series and ultra-thin CP-series.
Ultra-high pulse supercapacitors for GSM / GPS burst applications.
Custom battery packs qualified for oil, medical and industrial OEMs.
Our factory is certified to CE, UL, SGS, IEC, UN38.3, RoHS and ISO 9001, and we ship to operators in North America, Europe, the Middle East, Southeast Asia and Latin America.
7.2 What you get when you order the ER18505S from www.serui-battery.com
Application engineering support from day one. We help size strings, de-rate for your operating temperature, and select the right termination — before you cut metal.
OEM / ODM private label. The cell can ship with your brand laser-printed on the can, with custom heat-shrink and pack assembly.
Tiered pricing. Samples (1–50 pcs) for qualification, pilot runs (500–2,000 pcs), and volume pricing at 5K / 10K / 50K / 100K per quarter.
Stable supply. Three production lines dedicated to Li-SOCl₂ cells mean we can absorb demand spikes from oilfield customers without lead-time slippage.
Full documentation. Every shipment includes CoC, UN38.3 summary, MSDS and drawings — ready for your compliance and EHS teams.
7.3 A note on counterfeit risk
The LiSOCl₂ high-temperature market has its share of relabelled standard cells sold as "150 °C grade." The symptom is predictable: a cell that performs fine in the lab at 85 °C but leaks or goes silent after three days in a 150 °C downhole tool. SER controls its own electrolyte mixing, anode pressing and hermetic sealing, which is why our oilfield customers reorder the ER18505S quarter after quarter.
Conclusion: The High-Temperature Battery Problem, Solved
For any product that must survive the heat of a drilling rig, an autoclave cycle, a sun-baked container or a desert pipeline, the LiSOCl₂ battery is the only mature chemistry that combines a 3.6 V rail, 10-year shelf life and continuous operation at 150 °C. And within that chemistry, the ER18505S — 3.2 Ah, 18 × 50.5 mm, −30 to +150 °C, 1 A continuous / 2 A pulse — is the form factor most engineering teams already know how to design with.
If you are qualifying a downhole tool, a sterilisation data logger, a PIG or a desert GPS tracker, the ER18505S is the cell to put on your short list. Visit www.serui-battery.com to request a sample, download the full datasheet, or talk to our application engineering team about a custom high-temperature pack. We routinely ship free evaluation cells to qualified OEMs and turn around a formal quotation within 24 hours.
Power where the heat is. Reliably, for 10 years.
— The SERUI Team Guangzhou Serui Battery Technology Co., Ltd. www.serui-battery.com
