The heart of any portable electronics project is its power supply. Choosing the wrong battery can lead to burnt-out components, short runtimes, or even safety hazards. In this guide we break down the three most common rechargeable battery chemistries used by makers today: Li-Ion, LiPo, and LiFePO4.
1. Lithium-ion (Li-Ion)
The workhorse of the modern world. If you’ve ever held an 18650 cell, you’re familiar with lithium-ion technology. They are cylindrical, robust, and offer excellent energy density.
Key characteristics
- Nominal voltage: 3.6–3.7 V
- Max voltage: 4.2 V
- Common form factors: 18650, 21700 cylindrical cells
- Safety: moderate. Can vent with flame if abused.
Best for: projects requiring long battery life in a rigid enclosure, such as Bluetooth speakers, flashlights, and power banks.
2. Lithium polymer (LiPo)
LiPos are the performance kings. They use a polymer electrolyte which allows them to be made in flexible pouch shapes. Their main advantage is their incredible discharge rate (C-rating), allowing them to dump massive amounts of current instantly.
Key characteristics
- Nominal voltage: 3.7 V
- Max voltage: 4.2 V
- Common form factor: soft flat pouches
- Safety: low. Vulnerable to physical damage and overcharging.
Best for: high-performance applications like drones, RC cars, and wearable tech where weight and shape factor are critical.
3. Lithium iron phosphate (LiFePO4)
The safest of the bunch. LiFePO4 batteries sacrifice a bit of energy density for extreme durability and safety. They are chemically stable and have a completely different voltage curve.
Key characteristics
- Nominal voltage: 3.2 V
- Max voltage: 3.65 V
- Cycle life: 2000+ cycles (vs ~500 for Li-Ion)
- Safety: high. Extremely stable and resistant to thermal runaway.
Best for: solar-power storage, remote IoT stations, and projects where safety and longevity are more important than size.
Comparison at a glance
| Chemistry | Voltage (nominal) | Cycle life | Cost | Safety |
|---|---|---|---|---|
| Li-Ion | 3.7 V | 300–500 | Low | Medium |
| LiPo | 3.7 V | 300–500 | Medium | Low (careful!) |
| LiFePO4 | 3.2 V | 2000+ | High | High |
Summary & recommendation
For most beginner projects like a custom GameBoy or sensor node, stick with 18650 Li-Ion cells; they are cheap, easy to find holders for, and reasonably safe. If you are building a drone, you need LiPo. For a solar-powered weather station that needs to run for five years? LiFePO4 is your best friend.