TL;DR (simplified): Lithium batteries are dirty. Do not store empty or fully charged (recharge every ~6 months to ~50%). Dispose correctly, always salvage the BMS. Alkaline batteries will leak corrosive acid: do not leave them in stored devices.
The magic of batteries is to only use them where really necessary. Always make your batteries easily replaceable w/o tools! (Even Galaxy S5 phone could exchange battery and is water proof - there is no excuse)
Batteries will fail sooner or later. Don't be a crummy and make people throw away your product - think about the environment. Make your product to set battery/charging characteristics for minimum wear!
This is a short and comprehensive summary of things good to know about batteries and charging.
Fun fact: In German, a rechargeable battery is typically called “Akku”, the short form of accumulator.
Dispose of batteries correctly! For most countries there are collection boxes in supermarkets. Discharge batteries and tape off the poles of pouch cells and prismatic batteries.
Never just throw it into trash - there are daily fires on dumping grounds and batteries are DIRTY, polluting air&water; resources are lost.
Only because a lithium battery seems to be 0V on measuring, does not mean the cell does not hold any charge: the BMS probably disconnects the cell to protect the battery from further draining.
Consider to cut off the BMS and discharge the cell itself. To fully discharge, connect a load to the cell, e.g. a light bulb of a bike or a DC-motor (PC fan).
Lithium batteries are dirty on obtaining. Most lithium batteries use cobalt, which comes from the Democratic Republic of Congo (DRC), where mining is linked to:
Lithium itself also has an environmental strain too (water use, chemical pollution, land impact).
Always recycle and try to avoid in the first place. Try to think if battery is needed in your use-case or if you are fine with USB-C instead.
Just for clarification: Li-Ion refers to the broad chemistry family encompassing all rechargeable lithium-ion cells.
Li-Po is a type of Li-Ion cell that utilizes a pouch (polymer foil) casing.
All Li-Po are Li-Ion, but not all Li-Ion are Li-Po. The difference is packaging, not the fundamental chemistry.
Classic Li-Ion (cylindrical, prismatic) use a liquid electrolyte soaked into a separator.
Li-Po (pouch cells) originally meant polymer electrolyte (gel/solid-like), but in practice modern Li-Po still use liquid or gelled electrolytes, just packaged in a flexible foil pouch (sensitive to puncture/swelling) instead of a metal can (more robust packaging).
Listed are some common Li-Ion chemistries:
How lithium works: Lithium ions shuttle between the cathode and graphite anode during charge and discharge, storing and releasing energy.
Nominal Voltage is ~3.7 V per cell, 4.2 V per cell when fully charged.
First of all: Try not to quick charge if not necessary.
Terminology: “C” stands for the battery’s nominal capacity, and charging at 1C means supplying a current equal to the full capacity in one hour. For example, a 2000mAh battery charged at 1C would use 2000mA (2A) to fully charge in roughly one hour. The same applies to discharging.
| Charge Rate (C) | Approximate Cycle Life (Full Cycles) |
|---|---|
| 0.2 C | 1200+ cycles (longest lifespan, gentle charging) |
| 0.5 C | 800–1000 cycles (good balance of speed and lifespan) |
| 1.0 C | 500–700 cycles (standard fast charging) |
| 2.0 C | 300–500 cycles (faster charging, noticeable wear) |
| 3.0 C+ | <300 cycles (high stress, significant capacity loss) |
Charging above 1C regularly accelerates capacity fade. “C-rate stress” refers to both charging and discharging.
Heat generated at high rates is the main cause of wear.
Not all lithium batteries support >1C charging safely — always check manufacturer specs.
During quick charging, especially at high currents, lithium can start to plate as metallic lithium crystals (known as lithium dendrites) on the anode surface.
These dendrites:
That’s why fast charging increases safety risks and battery wear—because dendrite growth damages the battery’s internal structure.
Lithium batteries need chargers with special characteristics: A CC/CV charger with balance charges batteries in two stages, ensuring efficient and safe charging:
What is trickle charging? Trickle charging is feeding a battery a very small, low-current charge (often ~0.05–0.1 C) to slowly raise its voltage before normal charging.
For Li-Pos, it’s sometimes used to carefully bring a cell from slightly under-voltage (~3.0 V) back into a safe range — but it’s risky and not recommended below ~2.5 V per cell because internal damage may already be present, causing swelling and fire hazards.
Never charge a swollen battery, no matter the voltage!
Some devices allow to set the maximum charging percentage, like laptops. For Android there is ACCA in f-droid store (requires root), which allows to set charging speed too.
chemical aging is sped up If lithium batteries are stored at 100% State of Charge (SoC), which is ~4.2V.
When the voltage is that high (around 4.2 V per cell), the electrolyte and cathode are under more stress, which accelerates:
| Storage Voltage (per cell) | % State of Charge (SoC) (approx.) | Typical Lifespan Before Noticeable Capacity Loss |
|---|---|---|
| 4.20 V (100%) | ~100% | ~300–500 cycles |
| 4.00 V | ~85% | ~600–800 cycles |
| 3.85 V | ~50–55% | ~1,200+ cycles |
| 3.70 V | ~40–45% | ~1,500+ cycles |
| 3.50 V | ~25–30% | ~1,800+ cycles |
| <3.30 V | <15% | Risk of deep discharge damage |
That is why the “storage voltage” of ~3.7–3.85 V per cell is recommended (which is around ~50% SoC) — it minimizes stress while keeping enough charge to avoid deep discharge. Keep in a cool, dry place (ideally 15–25 °C). Self discharge of Li-Po is around ~2–3%/month (slightly higher than rigid Li-Ion (~1-2%)).
Check voltage every 6-9 months and recharge if voltage drops below 3.5V. Do not let it go below 3.3V!
Empty storing (aka forgetting the battery): Do not store lithium batteries empty. They die if voltage drops below 3.0V. Safe minimum under normal use is 3.3 V. Everything below 2.5V per cell is a danger zone (don’t attempt revival)! Do not attempt to trickle charge them for revival.
When voltage drops too low, copper from the anode can dissolve into the electrolyte. On recharge, this copper can plate back onto the cathode as tiny dendrites, which may pierce the separator and cause internal shorts — leading to swelling, overheating, or fire. Recycle deep discharged battery.
Always salvage the Battery Management System (BMS) board of a battery pack! You may still need it to re-cell (e.g. if no genuine aftermarket battery available).
Also, with the BMS it is possible to replace the battery with external power (for devices which would not turn on w/o battery) - nice for USB-C mods.
What is the purpose of a BMS?
Due to the protection feature it can be that you measure 0V on an empty battery - the cell itself can still have a charge. This does not necessarily mean that the cell is dead, it still can have ~3V and be safely rechargeable. When disposing of the battery, cut off the BMS and discharge the cell itself.
For DIY purposes there are charger modules on breakout boards. Compared below are a few common ones.
| Feature | TP4056 / TP4057 | TP4058 | TP5100 | IP2312 | IP2365 | IP5306-(I2C) |
|---|---|---|---|---|---|---|
| Type | Linear charger IC | Linear charger IC | Switching charger IC | Switching (buck) charger IC | Switching (buck) charger IC | PMU (charger + boost + power path) |
| Cells Supported | 1 Li-Ion/Li-Po (4.2 V) | 1 Li-Ion/Li-Po (4.2 V) | 1–2 Li-Ion/Li-Po (4.2 V / 8.4 V) | 1 Li-Ion/Li-Po (4.2 V / 4.35 V) | 1–4 Li-Ion/Li-Po (4.2 / 8.4 / 12.6 / 16.8 V) | 1 Li-Ion/Li-Po (4.2 V) |
| Input Voltage | 4–8 V (USB 5 V typical) | 4–8 V (USB 5 V typical) | 4.5–18 V | 4.5–6 V (USB-C, 5 V typical) | 4.5–26 V | 4.5–5.5 V (USB, micro-USB, Type-C) |
| Max Charge Current | Up to 1 A (set by resistor) | Up to 1 A (set by resistor) | Up to 2 A (set by resistor) | Up to 3 A (set by resistor) | Up to 3 A (set by resistor) | Up to 2.1 A (internally managed) |
| Efficiency | Low (linear, heats up >700 mA) | Low (linear, similar to TP4056) | High (switching, efficient) | High (~94–95%, switching) | High (~94–95%, switching) | High (switching, integrated boost) |
| Heat Dissipation | High at mid-high currents | High at mid-high currents | Much cooler at higher currents | Much cooler at high currents | Much cooler at higher currents | Efficient power path management |
| Trickle/Precharge | Yes (~100 mA <2.9 V) | Yes (~100 mA <2.9 V) | Yes (<2.9 V, low current start) | Yes (~100 mA <3.0 V) | Yes (low current start <3.0 V) | Yes (automatic precharge <3.0 V) |
| Termination | Automatic | Automatic | Automatic | Automatic (configurable) | Automatic (configurable) | Automatic |
| Protections | Thermal, safety timer | Thermal, safety timer, EN pin control | OVP, OCP, SCP, thermal | OVP, OCP, SCP, thermal | OVP, UVP, SCP, OCP, NTC, thermal, ESD | OVP, OCP, SCP, OTP, battery detection |
| Extra Features | Cheap, widely available | EN pin (MCU enable/disable charging) | Supports 2-cell packs, higher voltage | Adjustable current & cutoff voltage | Supports 1–4S packs, wide input range | Boost 3.7→5 V, load sharing, I²C control* |
| MCU Required | No | No | No | No | No | Optional (needed for advanced control) |
| MCU Can Be Useful | Monitor status pins | Toggle EN, read charge status | Monitor status pins | Toggle EN, monitor status LEDs | Toggle EN pin, monitor charge/fault pins | Full I²C communication and control* |
| Needs Heartbeat | No | No | No | No | No | Yes (to keep boost active at low load) |
Note: IP5306 needs heartbeat. Some modules need a fix for CD42 issue.
*Beware that only IP5306-I2C has I²C-bus (there is a plain IP5306 version too)! You can repurpose CD42 boards though. There is a repo with a lib for IP5306-I2C
IMO: For advanced products, see BQ-series of Texas Instruments: they have everything the heart desires.
Lithium Titanate Oxide (LTO) batteries use no cobalt.
| Feature | LTO (Lithium Titanate Oxide) | Li-Po (Lithium Polymer) |
|---|---|---|
| Nominal Voltage | ~2.4 V | ~3.7 V |
| Max Voltage | ~2.8 V | 4.2 V |
| Energy Density | Low (~60–80 Wh/kg) | High (~150–220 Wh/kg) |
| Cycle Life | Very high (10,000–20,000+ cycles) | Moderate (~300–1000 cycles) |
| Charge/Discharge Rate | Very high (10C+ possible) | Moderate to high (1–3C typical) |
| Self-Discharge | Very low (~1% per month or less) | Low (~2–3% per month) |
| Safety | Excellent (resistant to thermal runaway) | Moderate (risk of swelling/fire) |
| Cost | High | Moderate |
| Typical Applications | fast-charging applications | everything cheap or with high energy density |
https://en.wikipedia.org/wiki/Lithium-titanate_battery
Read about open source BMS on hackaday.com
Alkaline batteries cannot be recharged and pose an environmental hazard when discarded.
They have 1.5V when full. How to tell if an alkaline battery is full or empty without measuring it?
If you drop a battery upright onto a hard surface, an empty battery will bounce higher than a full one. This happens because the electrolyte inside an empty battery has dried and hardened.
It is similar to spinning an egg: a raw egg wobbles because the inside is liquid, while a cooked egg spins smoothly because it is solid.
Hardened electrolyte will cause leaks, which is why batteries have a “best before date” (BBD). The leaking battery acid is corrosive, damaging the contacts in your device. Do not leave batteries in stored away devices.
If your contacts are corroded, clean them and apply solder tin, so they stop corroding (bc electroplating is too complex).
Ni-MH (Nickel-Metal Hydride) batteries are rechargeable and behave quite differently from lithium batteries when they are depleted or overcharged. They have a long life span, as there is no significant memory effect
When Nickel batteries are fully charged, they have 1.2V, which sometimes is a problem when a device expects 1.5V from an alkaline battery (=bad product design). For that purpose there are Li-Po batteries in form factor of AA/AAA with 1.5V voltage regulator inside (and USB-C for charging).
When Ni-MH is depleted:
When overcharging:
Structure of Ni-MH:
Ni-MH has replaced Ni-Cd (Nickel-Cadmium) batteries for home use. Ni-Cd are only found in specific industrial applications nowadays.