Lithium Batteries
by Don Apostolico
This article addresses misinformation and concerns many aeromodelers have about Lithium-ion (Li-ion) and Lithium Polymer (Li-Poly) batteries, and the practices that cause batteries to prematurely fail, self-combust, or vent (swell up like a balloon).
Consider the hundreds of millions of people around the world who are, at this moment, safely operating Lithium-powered consumer electronics without issue: cell phones, MP3 players, iPods, laptop computers, some Dremel tools, GPS systems, garden power tools, cordless drills, hearing aids, digital cameras, and camcorders.
Contrast that image with the modeling community, which is often required to charge batteries in ammunition or ceramic safety boxes in case batteries vent or combust while charging. Why can Grandma Jones charge a consumer 5000 mAh Lithium battery on the kitchen table, while many modelers place batteries in fortified enclosures? The reasons become clear below.
The current aeromodeling mindset about Lithium battery danger has been shaped by lack of information, misinformation, product misuse, uninformed opinions, reporting symptoms rather than diagnosing causes, and blaming the battery instead of identifying the root cause. Incidents do occur, but Lithium is only one of many power sources that can combust if handled or charged incorrectly. Improper charging and handling, random failures, and lack of understanding often result in mishaps. Monitoring and caution are prudent for all batteries—not only Li-ion or Li-Poly.
Consumers vs. Modelers: different charging requirements
As far as I have seen, aeromodelers are often the only group lawyers require to charge batteries in a safety container outside the aircraft. That practice is not wrong, but consumer-product users are usually required, by design, to use the correct supplied charger. Those chargers are programmed to the correct charge rate and calibrated to the proper milliamps/voltage and cell configuration. Modelers, by contrast, commonly use adjustable chargers and can select incorrect voltage, amperage, chemistry, cell count, or wiring configurations.
Grandma Jones cannot dial in the wrong voltage/amperage, select the wrong battery chemistry, or use the wrong cell configuration when charging her phone. Modelers can. A lack of operational knowledge makes any electrical device more hazardous. The good news is that education can address most safety issues.
Following are the major operational issues with aeromodelers' Lithium batteries.
Compatibility
Not all Lithium chargers are compatible with all brands or constructions of Lithium batteries. If you have doubts about your charger, check the instructions or call the charger manufacturer before plugging it into your battery.
Dumb vs. Smart Chargers and Batteries
- A "dumb" charger has no ability to regulate the charge rate or manage cell balancing.
- A "dumb" battery has no protective circuitry onboard.
- A "smart" battery includes an integrated circuit that regulates charge rate and often includes protection such as a circuit breaker or cell-balancing.
- A "smart" charger allows the user to select cell count, voltage, current rates, chemistry, time, or cutoff voltage and can monitor charging conditions.
If you use a dumb charger on a dumb Lithium battery with incorrect settings, you can cause overheating, venting, or fire.
Caution! You must use correctly programmed, compatible chargers for the specific battery size, capacity, cell count, and wiring configuration. Do not leave batteries unattended while charging. A slower charge rate is generally more battery-friendly than fast-charging.
Smart batteries have fallen into disfavor with some modelers who fly large aircraft because an internal protective device could trip under high-G maneuvers. Smart chargers and batteries offer safety but require understanding of their behavior and limitations.
Wiring configuration
Batteries can be wired in series, parallel, or in series-parallel. You must know your pack's configuration to safely charge it.
Example: Four-cell Lithium packs wired series-parallel may be charged as a two-cell pack on the 7.4 V setting. If you mistakenly charge a four-cell series-parallel pack on the four-cell (14.8 V) setting, you can start a fire.
This is an operator error, not a battery defect. Familiarize yourself with basic electrical wiring and cell configurations before making connections.
Current settings and programming errors
Many modelers use high-end programmable chargers and then think they have defective batteries when a pack vents or bursts during charging. Often the cause is an incorrect charge procedure: wrong voltage, wrong amperage, wrong chemistry, or an incorrect decimal entry. For example, entering 5.0 A instead of 0.5 A on a charger can overcharge and catastrophically heat a pack within minutes.
Understand your charger's programming procedure and double-check all entries before starting a charge.
High charge rates and heat
Heat is the enemy of all batteries. Many Lithium packs are rated for a 1C charge rate (where 1C equals the pack capacity in amperes). For example, a 2000 mAh pack at 1C charges at 2.0 A and will get warm; charging at higher rates generates more heat and stresses cells.
A slower charge rate reduces heat, increases reliability, lengthens battery life, and reduces the likelihood of malfunctions. Li-Poly packs typically should not become hot when charged at their rated 1C; if they do, discontinue use of that pack.
In practice, I charge large packs much slower than their rated maximum. For example, I charge a 5200 mAh Li-ion pack at 1.0 A instead of 5.2 A. It takes longer, but the pack lasts far longer—often years and many flights—compared with fast-charging that can shorten pack life to a few months.
Other common mistakes and operator issues
Don's Hobby Shop has sold and equipped giant-scale models with Lithium batteries since 1996. From that experience, the primary mistakes I see are:
- Using incompatible chargers.
- Setting incorrect charge rates.
- Using "dumb" chargers with "dumb" batteries incorrectly.
- Selecting the wrong settings on adjustable "smart" chargers.
- Exceeding the battery's discharge current capacity.
- Fast-charging batteries beyond their rated capacity.
- Improperly securing batteries so they vibrate or shift.
- Subjecting batteries to shock impact (crashes) and reusing damaged packs.
The result of these errors is often a fire, which is a symptom of operator error rather than a battery defect. A pack labeled "defective" after a failure is often only the final symptom; the true cause is usually misuse or improper setup.
Mechanical damage and reuse
Batteries that shift during flight can contact hard surfaces, CA or epoxy shards, or formers that puncture cells and cause shorting or venting. Hard-mounting without shock-absorbing foam can lead to cell puncture. A battery that has received impact damage should never be reused. Internal damage can result in a delayed short that may occur after several charge cycles and flights, leading to sudden catastrophic failure later.
This problem is analogous to burning up a digital servo because the operator set travel incorrectly and overdriven a throttle. The correct response is education and proper setup, not avoiding the technology.
Recommendations and final thoughts
- Read and understand the programming procedure for your charger before connecting it to a battery.
- Use chargers and batteries that are compatible. If unsure, consult the manufacturer.
- Charge at reasonable rates; slower is safer and kinder to the pack.
- Do not exceed a pack's discharge rating—buy a pack sized for your model's current requirements.
- Secure batteries properly with appropriate foam or restraints to prevent vibration damage.
- Never reuse a battery that has been impacted or physically damaged.
- Monitor charging; do not leave packs unattended.
- Educate yourself and fellow modelers. Operator error is the leading cause of battery incidents.
Handling, storing, and charging any battery incorrectly can lead to problems. Exercise caution with all battery types, and don't confuse excellent piloting skills with technical battery expertise. Take responsibility to learn and apply safe practices.
Have fun and fly safely.
Don Apostolico [email protected]
Sources
- Don's Hobby Shop
(800) 972-6273 www.donshobbyshop.com
- Fromeco Scale Avionics
(503) 715-0020 www.fromeco.org
- Great Planes
(217) 398-8970 www.greatplanes.com
Transcribed from original scans by AI. Minor OCR errors may remain.
