SuperPower Battery — Next-Gen Power Tool Battery Project

Problem Statement

Why Replace 18650?

The Li-ion 18650 battery, the current standard in the power tool market, has fundamental limitations. We diagnose the 4 key problems experienced at job sites.

⏱

Charging Time Problem

1-4 hours of charging wait time is the biggest bottleneck disrupting workflow. Workers need to carry 2-3 spare batteries, and at outdoor job sites without power infrastructure, work interruption is inevitable.

1-4 hour wait → Work interrupted

🔄

Lifespan Limitation

Capacity drops sharply after 500 charge-discharge cycles. Professional users must replace batteries every 1.5-2 years, incurring recurring costs of $50-80 per pack.

500 cycles → Replace every 2 years

🔥

Safety Risk

There is a risk of thermal runaway during heavy-load operations. Cell swelling, electrolyte leakage, and in extreme cases fire can occur, with increased risk in enclosed spaces or high-temperature environments.

Thermal runaway · Swelling · Fire risk

❄

Temperature Limitation

Output drops by more than 50% below -10°C. Reliability significantly decreases in cold environments such as winter outdoor work, cold storage, and high-altitude areas.

Below -10°C → 50% performance drop

Key Insight: These 4 problems stem from the chemical characteristics of lithium-ion cells and cannot be fundamentally solved by BMS improvements alone. The cell chemistry itself must be replaced.

Technology Analysis

Technology Comparison: 4 Types of Energy Storage

Quantitatively comparing 3 alternative candidates (LTO, EDLC, LIC) against the Li-ion baseline. Practical specs are calculated based on an 18V power tool pack.

Li-ion (18650)

LTO (Lithium Titanate)

EDLC (Supercapacitor)

LIC (Lithium-Ion Capacitor)

Item	Li-ion (18650)	LTO (Lithium Titanate)	EDLC (SuperCap)	LIC (Li-ion Cap)
Energy Density	250 Wh/kg	50-80 Wh/kg	5 Wh/kg	15-20 Wh/kg
Power Density	1,000 W/kg	3,000 W/kg	10,000 W/kg	5,000 W/kg
Charge Time	1-4 hours	6-15 min	1-10 sec	1-5 min
Lifespan (Cycles)	500	5,000-20,000	1,000,000+	100,000+
Cell Voltage	3.6V	2.4V	2.7V	3.8V
Self-Discharge/mo	2-5%	3-5%	5-40%	5-10%
Temp Range	-10~45°C	-40~55°C	-40~65°C	-20~60°C
Safety	Medium	High	Very High	High
18V Pack Weight	0.7 kg	1.5 kg	3.6 kg	2.5 kg
18V Pack Runtime	30 min	12-15 min	2-7 min	8-10 min
Price (Pack)	&won;50,000	&won;80,000-120,000	&won;150,000+	&won;120,000+

Analysis Conclusion: Li-ion is dominant in energy density but inferior in charging/lifespan/safety. LTO is the most balanced alternative, while EDLC specializes in extreme power/lifespan. LIC occupies the middle ground between the two technologies. — For power tool applications, LTO standalone or LTO + SuperCap hybrid are the optimal candidates.

Overall Suitability Score (18V Power Tool Pack Basis)

Li-ion

5.5

LTO

7.8

EDLC

6.2

LIC

7.0

* Overall Suitability = Weighted average of (Energy×0.25 + Power×0.2 + Charge Speed×0.25 + Lifespan×0.15 + Safety×0.15)

Plan A

LTO Battery Pack

Toshiba SCiB LTO cell-based · Ultra-fast charging · 20,000 cycle lifespan · Extreme environment tolerance

3-1. LTO Cell Configuration

8S Configuration — 20V MAX Tool Compatible

7S Configuration — 18V Tool Compatible

LTO Cell Options:
Prismatic: Toshiba SCiB 23Ah — High capacity, for heavy-duty tools
Cylindrical: 18650/21700 LTO 1.5~3Ah — Compact pack, for light-duty work

3-2. BMS Circuit Block Diagram

3-3. Fast Charging Circuit

Dual Charger Rationale: A single BQ24600 IC supports up to 4S. To charge an 8S pack, two BQ24600s independently charge each 4S group. The two groups are connected in series to form the full 8S (19.2V nominal). This architecture also improves cell balancing efficiency.

3-4. Performance Specifications

Item	8S LTO Pack	7S LTO Pack
Nominal Voltage	19.2V	16.8V
Full Charge Voltage	22.4V (8 x 2.8V)	19.6V (7 x 2.8V)
Discharge Cutoff Voltage	12.8V (8 x 1.6V)	11.2V (7 x 1.6V)
Capacity (Prismatic 23Ah)	23Ah / 441Wh	23Ah / 386Wh
Capacity (Cylindrical 3Ah)	3Ah / 57.6Wh	3Ah / 50.4Wh
Continuous Discharge Current	10C (23A ~ 230A)	10C (23A ~ 230A)
Charge Current	5~10C	5~10C
Charge Time	6-12 min	6-12 min
Cycle Life	20,000+	20,000+
Operating Temperature	-40 ~ 55 °C	-40 ~ 55 °C
Pack Weight (Prismatic)	~2.8 kg	~2.5 kg
Pack Weight (Cylindrical)	~0.6 kg	~0.5 kg

3-5. BOM (Bill of Materials)

Component	Model	Qty	Unit Price (USD)	Subtotal	Role
LTO Cell	Toshiba SCiB 23Ah	8	$15	$120	Energy Storage
BMS IC	TI BQ76940	1	$6	$6	Cell Monitoring
FET Driver	TI BQ76200	1	$4	$4	Protection FET Driver
Charger IC	TI BQ24600	2	$5	$10	CC/CV Charging
N-MOSFET	IPP075N15N3	4	$2	$8	Charge/Discharge Switching
Shunt Resistor	5mΩ	1	$1	$1	Current Sensing
NTC Thermistor	10kΩ	2	$0.5	$1	Temperature Sensing
MCU	MSP430G2553	1	$4	$4	Control / Communication
Inductor	10µH 15A	2	$3	$6	Charger Inductor
Capacitors	Various (MLCC/Elec)	20	$0.5	$10	Filter / Decoupling
Resistors / etc	Various (0402~0805)	30	$0.1	$3	Balancing / Pull-up
PCB	4-layer FR4 (2oz Cu)	1	$8	$8	PCB Board
Connector	Tool-specific	1	$3	$3	Tool Connection
Housing	ABS injection mold	1	$5	$5	Case
AC Adapter	24V/10A 240W	1	$15	$15	Charger
TOTAL (8S Prismatic Pack)				~$204	BOM Cost

BOM Note: The prices above are based on small quantity (1-10 units) purchase. For bulk orders of 100+ units, cell unit price drops to $8-10, reducing total BOM to $140-160. Using cylindrical cells, cell cost is $5 x 8 = $40, bringing total BOM to ~$124.

3-6. Plan A Pros & Cons Summary

Advantages

CHARGE

10-Minute Ultra-Fast Charge

5-10C charging capable. 10x faster than Li-ion. Fully charged in the time of one coffee break.

CYCLE

20,000+ Cycle Life

Even with 3 charges/day, lasts 18 years. 40x+ vs Li-ion 300-500.

TEMP

-40~55 deg C Operation

Capable in extreme cold. No performance degradation in winter outdoor work, cold storage, etc.

SAFETY

No Thermal Runaway (Intrinsic Safety)

LTO anode (Li4Ti5O12) requires no SEI layer. No fire even during nail penetration/overcharge.

POWER

High Power Output (10C Continuous)

230A continuous discharge with 23Ah cells. Suitable for high-load tools like grinders/impact drivers.

Disadvantages

ENERGY

Low Energy Density

~65 Wh/kg (Li-ion ~250 Wh/kg). About 1/3 capacity in the same size. Shorter work time.

COST

High Initial Cost

BOM ~$204 (2-3x vs Li-ion pack). However, TCO favors LTO when accounting for lifespan.

WEIGHT

Weight Increase

Prismatic pack ~2.8kg (30-50% heavier than equivalent Li-ion). Causes fatigue during prolonged manual work.

VOLTAGE

Voltage Platform Difference

2.4V per cell (vs Li-ion 3.6V). More cells needed for the same voltage (8S vs 5S for 20V).

SUPPLY

Limited Cell Supply

Toshiba SCiB monopoly. AliExpress/Yinlong alternatives have variable quality. Not as easy to source as regular 18650.

TCO (Total Cost of Ownership) Comparison

Li-ion 18650 Pack

$80

x 500 cycles = 40 packs

$3,200

20-year TCO

LTO Pack (Plan A)

$204

x 1 unit (20,000 cycles)

$204

20-year TCO

Savings

93.6%

$2,996 saved

20-year basis

——— End of Section 3: Plan A — LTO Battery Pack ———

Plan B

Hybrid (Supercap + Li-ion)

A hybrid power system combining the explosive burst output of supercapacitors with the stable energy density of lithium-ion. Achieves both 30-second quick-ready and 15+ minutes continuous work simultaneously.

4-1. Hybrid System Architecture

Core Concept: The supercap serves as the "primary power source" handling instantaneous loads, while lithium-ion acts as "backup + charging source" to refill the supercap. The moment you pull the drill trigger, the supercap instantly delivers 190A; the moment you release it, Li-ion refills the supercap via DC-DC.

4-2. Energy Flow Diagram — 4 Operating Modes

4-Mode Auto Switching: The MCU (MSP430) monitors load in real-time via current sensor (INA219), switching modes at millisecond intervals based on load changes. The user needs to do nothing.

4-3. Charging System — Dual-Path Charging

Quick Ready Practicality: When the battery dies at the job site, just plug in for 30 seconds and the supercap (2.5Wh) is full. This energy provides dozens of drill shots and impacts immediately. The Li-ion can be fully charged during lunch break (90 minutes) at the office.

4-4. Hybrid Control Logic — Flowchart

4-5. Performance Specifications

Item	Hybrid Pack Specifications
Nominal Voltage	18V
Supercap Energy	2.5Wh (7S × 350F EDLC)
Li-ion Energy	55.5Wh (5S × 3Ah @ 3.7V)
Total Energy	58Wh
Peak Burst Output	3,500W Supercap Burst
Continuous Output	360W Li-ion Sustained
Quick Charge	30 sec (supercap only)
Full Charge	90 min (Li-ion + supercap)
Continuous Runtime	15-20 min (Li-ion basis)
Burst Runtime	~2 min (supercap only, full burst)
Lifespan	Supercap 1,000,000 cycles / Li-ion 500
Operating Temperature	-30 ~ 55°C
Pack Weight	~1.2 kg
Pack Size	Approx. Makita 6Ah battery pack size

4-6. BOM (Bill of Materials)

Component	Model	Qty	Unit Price (USD)	Subtotal
Supercap	Maxwell BCAP0350 2.7V 350F	7	$8.00	$56.00
Li-ion Cell	Samsung INR18650-30Q	5	$4.00	$20.00
DC-DC	TI LM5176	1	$10.00	$10.00
Li-ion BMS	BQ76930 (6-10S)	1	$6.00	$6.00
SC Balancer	Resistive (10Ω each)	7	$0.10	$0.70
Charger IC	BQ24600	1	$5.00	$5.00
MCU	MSP430G2553	1	$4.00	$4.00
MOSFETs	Various (N-ch / P-ch)	6	$2.00	$12.00
Inductor	22µH 20A shielded	1	$4.00	$4.00
Current Sensor	INA219	2	$3.00	$6.00
Caps / Resistors	Various passives	40	$0.30	$12.00
PCB	4-layer FR4	1	$10.00	$10.00
Connector	Tool-specific (Makita/DeWalt)	1	$3.00	$3.00
Housing	ABS injection mold	1	$5.00	$5.00
AC Adapter	24V / 5A (120W)	1	$12.00	$12.00
TOTAL				~$166

Cost Analysis: $50-60 more than Plan A (supercap only), but energy capacity increases from 2.5Wh to 58Wh — a 23x increase. Cost per Wh actually improves dramatically from $44/Wh to $2.86/Wh.

4-7. Pros & Cons Analysis

Pros

1	30-Second Quick Ready Just 30 seconds of supercap charging and you can start immediately. No Li-ion charging wait needed.
2	3x Instant Torque Supercap 190A burst → 3,500W. 10x instant output compared to pure Li-ion (20A, 360W).
3	Regenerative Charging Instantly recovers motor braking energy to supercap. 95%+ efficiency, impossible with Li-ion alone.
4	Extended Li-ion Lifespan Supercap handles burst current → Li-ion load shared → Cell degradation reduced → 2x+ lifespan.
5	Wide Operating Temperature -30~55°C. Supercap operates normally even in midwinter outdoor work (compensates for Li-ion's -20°C limit).
6	Practical Runtime 55.5Wh Li-ion → 15-20 min continuous work. Equivalent to Makita 3Ah battery.

Cons

1	Increased Circuit Complexity Bidirectional DC-DC + MCU + Dual BMS. 2x component count vs Plan A, firmware development required.
2	Dual Energy Source Management Must simultaneously manage supercap voltage + Li-ion SOC. Mode switching logic stability verification needed.
3	Li-ion Lifespan Limitation Remains Supercap lasts 1M cycles, but Li-ion portion still has 500 charge/discharge cycle limit (2-3 years).
4	Weight Increase 1.2kg. Heavier than Plan A (0.85kg), but only +0.5kg compared to existing battery packs (0.7kg).
5	Cost Increase $166 (+$60 vs Plan A). Mass production target $120 possible, but 2-3x existing battery $40-60.
6	Development Timeline Firmware + PCB + thermal design + safety certification. Estimated 3-6 months to prototype.

Plan B Overall Verdict

58 Wh

Total Energy

23x vs Plan A (2.5Wh)

3,500W

Peak Burst Output

10x vs existing Li-ion

$166

Prototype Cost

Mass production target $120

Conclusion: Plan B is the most realistic approach that captures both practicality and innovation simultaneously. By combining supercap burst power with Li-ion energy density, achieving "30-Second Quick Ready + 20-min continuous work + 3,500W burst output" a performance combination impossible with existing power tool batteries. However, given the circuit complexity and firmware development burden, start with Plan A as MVP, then expand to Plan B after validation — a phased approach is recommended.

Compatibility

Power Tool Compatibility

5-1. Major Brand Battery Specifications

A table summarizing the voltage ranges and LTO/hybrid series configurations for each power tool battery platform on the market. Calculated based on LTO nominal 2.4V, supercap 2.7V, and Li-ion 3.6V.

Brand	Series	Nominal V	Actual V Range	Connector	LTO Config	Hybrid Config
Makita	18V LXT	18V	15 ~ 21V	Slide 5-pin	8S (19.2V)	7S Cap + 5S Li
DeWalt	20V MAX	18V (marketing 20V)	15 ~ 20.5V	Rail slide	8S (19.2V)	7S Cap + 5S Li
Milwaukee	M18	18V	15 ~ 21V	Slide	8S (19.2V)	7S Cap + 5S Li
Bosch	18V	18V	15 ~ 21V	Slide	8S (19.2V)	7S Cap + 5S Li
Ryobi	ONE+ 18V	18V	15 ~ 21V	Slide	8S (19.2V)	7S Cap + 5S Li
Makita	40V XGT	36V	30 ~ 41V	Slide	16S (38.4V)	14S Cap + 10S Li
DeWalt	60V FLEXVOLT	54V	45 ~ 60V	Rail	24S (57.6V)	21S Cap + 15S Li
Milwaukee	M12	12V	10 ~ 13.2V	Slide	5S (12V)	4S Cap + 3S Li

NOTE: DeWalt "20V MAX" is a marketing designation; the actual nominal voltage is identical to 18V (5S Li-ion). The LTO 8S configuration (19.2V) reaches 21.2V at full charge, within the voltage range of all 18V platforms.

5-2. Adapter Plate Concept

A universal design concept where the main PCB remains identical, with only brand-specific adapter plates being swapped.

Performance

Performance Comparison Charts

6-1. Comparison by Usage Scenario

Comparing relative performance of LTO and Hybrid against Li-ion as the 100% baseline. The reason Hybrid exceeds 120% in impact work is due to the supercap's instantaneous high-current supply capability.

INSIGHT: The reason Hybrid exceeds Li-ion (120%) in impact work is because the supercap can instantaneously supply over 100A of high current. In continuous work (cutting, etc.), Li-ion prevails due to energy density differences.

6-2. Charge Time Comparison

6-3. Total Cost of Ownership (TCO) 5-Year/10-Year Comparison

Initial cost is higher for LTO/Hybrid, but near-zero replacement costs lead to long-term reversal.

Item	Li-ion	LTO	Hybrid
Initial Purchase (2 packs)	$100	$408	$332
Replacement Cost (5 years)	$300 (6 replacements)	$0	$40 (1 Li-ion replacement)
Charging Electricity	$15	$15	$15
5-Year Total Cost	$415	$423	$387 BEST
10-Year Total Cost	$830	$423 BEST	$427

KEY FINDING: At the 5-year mark, Hybrid ($387) is the most economical. At the 10-year mark, LTO ($423) is the most economical with $0 replacement costs. Li-ion has a low initial cost but requires replacement every 2 years, doubling long-term costs.

Case Design

Case Design Concept

7-1. Plan A: LTO Pack Cross-Section

Based on Makita 18V size (~130 x 75 x 65mm)

7-2. Plan B: Hybrid Pack Cross-Section

Slightly larger case (~140 x 80 x 70mm)

Roadmap

Project Roadmap

Phase	Duration	Work Items	Deliverables
1. Design	2 weeks	Circuit design (BMS + DC-DC + Protection), PCB layout, simulation	KiCad schematic + PCB files
2. Prototype	3 weeks	PCB ordering/fabrication, component mounting (SMT + THT), initial operation verification	Working Board (Bare Board)
3. Case	1 week	3D print case design + print, adapter plate fitting	STL files + assembled product
4. Testing	2 weeks	Performance measurement (capacity/current/temp), safety test (overcharge/short circuit/drop)	Test Report
5. Optimization	2 weeks	Firmware tuning, thermal management improvement, charge/discharge algorithm optimization	Final Firmware (.hex/.bin)
6. Documentation	1 week	Build guide, specifications, circuit description, BOM, assembly manual	Technical documentation (Open Hardware)

Total Duration

11 week

Approx. 3 months

Estimated BOM Cost

~$200

Per prototype set

PCB Layers

4L

4-layer (high current)

License

OSHW

Open Source Hardware