Why chemistry matters for remote devices
A remote sensor may sit for years in a freezer, on a roof or in a field, and nobody wants to visit it often. In that situation the chemistry inside the cell matters as much as its size. Different chemistries behave very differently when they are cold, when they sit unused, and when asked for a short burst of current.
This article compares the general families in plain terms. Exact figures vary by manufacturer and model, so treat everything here as typical behavior and check a cell’s datasheet before relying on it.
First question: primary or rechargeable
The most important split is between cells you throw away when empty (primary) and cells you recharge (secondary).
- Primary cells usually hold more energy for their size, lose little charge while idle, and need no charging circuitry. They suit devices that draw very little and are expected to run for years.
- Rechargeable cells suit devices with a power source nearby, such as solar, or devices used heavily, such as wearables. They need a charger, tend to lose charge faster when idle, and wear out after a limited number of cycles.
If a device draws so little that a primary cell would last for years, a rechargeable cell and its charging circuit usually add cost and complexity without much gain.
Common primary chemistries
Alkaline. These are the familiar household cells. They are inexpensive and widely available. They work reasonably at room temperature but typically lose performance in the cold, and their voltage declines steadily as they empty, which can confuse devices that expect a steady voltage. They also have a risk of leaking if left in an empty device for a long time. They suit indoor sensors with modest demands.
Primary lithium. These cells, often in coin or cylindrical form, generally have a long shelf life, hold up better in both cold and heat than alkaline cells, and keep a fairly flat voltage until near the end. Many designs for sensors expected to run for years are based on them. Within this family, some types are better at delivering short high-current pulses than others, and that matters because a radio transmission is exactly such a pulse. A small coin cell may have trouble with a strong transmission burst, which is why some designs add a small capacitor alongside it.
Lithium thionyl chloride types. A particular kind of primary lithium cell known for very low self-discharge and a wide temperature range, often chosen for long-life utility and outdoor devices. Their ability to supply large bursts may be limited, and some designs pair them with a storage capacitor. Check the specification carefully.
Common rechargeable chemistries
Lithium-ion and lithium polymer. These pack a lot of energy into a small space and are the usual choice for wearables, phones and many portable devices. Cautions: they usually should not be charged below freezing, they age with time and heat, and they require a proper charge controller and protection circuit. Damaged cells can be a fire hazard, so they should be handled and disposed of carefully.
Lithium iron phosphate. A lithium-based rechargeable type often considered tolerant of many charge cycles and more thermally stable than other lithium-ion types, though with less energy for its size. It is sometimes chosen for solar-powered outdoor devices, though it too usually has limits on charging in the cold.
Nickel-metal hydride. Common in rechargeable versions of household batteries. These cells tolerate a wide range of uses, but the standard types lose charge relatively quickly when sitting idle, and some low-self-discharge versions reduce that. They are less ideal for devices that must sit untouched for months.
Lead-acid. Found in larger installations such as pole-mounted equipment or backup systems. Heavy but robust, with a long history, and usually inexpensive per unit of energy. Not suitable for small devices.
Supercapacitors. Technically not batteries, but often used alongside them or alongside energy harvesting. They can deliver bursts and recharge quickly, but hold little energy and drain relatively fast, so they are for bridging short gaps rather than months of storage.
Comparing the families
| Type | Shelf life | Cold and heat | Rechargeable |
|---|---|---|---|
| Alkaline | Moderate | Weaker in cold | No |
| Primary lithium | Long | Generally good | No |
| Lithium-ion / polymer | Loses charge and ages | Charging limited in cold | Yes |
| Lithium iron phosphate | Reasonable | Charging limited in cold | Yes |
| Nickel-metal hydride | Shorter when idle | Moderate | Yes |
| Lead-acid | Needs topping up | Moderate | Yes |
These are broad generalizations, not guarantees.
Matching chemistry to the job
- Indoor sensor, replaced occasionally: alkaline or a primary lithium coin cell.
- Outdoor sensor in a cold climate, years between visits: a primary lithium type with good low-temperature performance, with a pulse-handling plan for the radio.
- Wearable or handheld device: a small rechargeable lithium-based cell with a built-in charger.
- Solar device: a rechargeable cell with a charge controller that stops charging when it is too cold, or a supercapacitor and cell combination; see the article on solar powered sensors for sizing.
- Backup for a mains device: a small rechargeable cell kept topped up, replaced on a schedule.
Other points to check
- Pulse capability. Ask whether the cell can supply the short peaks your radio needs, not just the average current.
- Voltage range. The device’s electronics must tolerate the cell’s voltage from full to empty.
- Self-discharge. For a ten-year goal, quiet losses matter.
- Transport and shipping rules. Lithium cells often have rules for shipping and storage that vary by region.
- Disposal. Every chemistry here should be recycled where facilities exist, not put in household trash; our article on electronic waste covers preparation.
The best chemistry is rarely the one with the highest advertised capacity. It is the one that still works on the coldest night of the year, after years on the shelf, at the moment the radio fires.