An attempt to start an internal combustion engine by connecting a lithium-ion battery from a power tool to the starter is doomed to failure due to the colossal difference in starting currents. Standard car battery 12V 55Ah capable of delivering 400–600 Amperes for a short time, while the maximum discharge current of even a powerful battery Makita or Bosch at 18 volts it rarely exceeds 30–50 Amps without instantaneous overheating and failure. The physical laws of electrodynamics do not allow the low capacity and internal resistance of the screwdriver battery to turn the flywheel of an engine with a volume of more than 1 liter, especially in winter.
In theory, if you connect several batteries in series, you can get the required voltage, but the current will remain critically low for operation starter. An attempt to implement such a scheme in practice will only lead to a deep discharge of an expensive instrument and a possible fire of its electronics. In this article, we'll take a closer look at why this method doesn't work, what viable alternatives exist, and how to properly use portable jump starters, which are often confused with screwdriver batteries.
Physics of the process: why 18 volts is not enough
Many car enthusiasts mistakenly believe that the main thing in starting an engine is voltage, so the idea is to use a battery 18V seems like a logical replacement for the regular one 12V battery. However, for the operation of the starter motor, the critical parameter is the current strength, and not just the voltage. Screwdriver batteries, whether Ni-Cd or Li-Ion, are designed to deliver a moderate amount of current over a long period of time the tool's motor is running, rather than releasing enormous energy instantly.
The internal resistance of a car battery is measured in hundredths of an ohm, which allows it to deliver hundreds of amperes without a significant voltage drop. At the same time, the screwdriver battery has a significantly larger internal resistance. When you try to connect it to the starter, the voltage at the terminals will instantly drop to several volts, which is absolutely not enough to create a magnetic field in the starter windings.
⚠️ Warning: An attempt to forcefully short the screwdriver battery contacts to the starter terminals may lead to thermal discharge of the lithium cells, their swelling or even explosion.
Additionally, the battery management system (BMS) in modern tools DeWalt, Milwaukee or Makita Has built-in overcurrent protection. If a sharp jump in consumption, characteristic of the starter, is detected, the controller will simply turn off the power and the engine will not make even one revolution.
Technical specifications: comparison of energy sources
To understand the scale of the problem, it is necessary to compare the technical parameters of a car battery and a typical power tool battery. The difference in energy consumption and current efficiency becomes obvious when examining the specifications in detail. Automotive AKB (Acid Battery) is designed to work in extreme conditions of the engine compartment and high loads.
A screwdriver battery, even the most powerful, is designed for periodic operation of a drill or impact wrench, where consumption peaks are smoothed out by the mechanical inertia of the chuck. The table below provides a comparison of key parameters, explaining the impossibility of directly replacing one energy source with another.
| Parameter | Car battery (55 Ah) | Screwdriver battery (18V, 5 Ah) |
|---|---|---|
| Rated voltage | 12 Volt | 18-20 Volt |
| Starting Current (CCA) | 450-600 Amps | 30-60 Amps (max) |
| Internal resistance | 0.005 - 0.01 Ohm | 0.05 - 0.1 Ohm |
| Weight | 14-16 kg | 0.6 - 0.8 kg |
As can be seen from the data, the starting current of the tool battery is 10-15 times lower than the required minimum. Even if you theoretically connect several batteries in parallel, synchronizing their operation without sophisticated electronics is impossible, and the risk of damage to the BMS remains one hundred percent.
The main idea: Directly connecting the screwdriver battery to the car starter is technically impossible and dangerous for the tool itself.
Portable jump starters: confusion of concepts
Often the reason for the question of starting from a screwdriver is the visual similarity of compact lithium boosters (starting devices) with power supplies for power tools. Modern Jump Starter They do use lithium polymer or lithium iron phosphate cells, similar to those found in screwdrivers, but their internal design is radically different.
A special board is installed inside the booster, capable of briefly delivering a current of 400-1000 Amps, which a conventional battery does not have. 18V. In addition, the boosters have protection against polarity reversal and short circuit, adapted specifically for automotive networks. Some models even have replaceable battery packs, but they are not compatible with power tool platforms due to different communication protocols.
Users sometimes try to convert the battery from a screwdriver into a starting device by adding crocodiles directly to the contacts. This is a gross mistake, since without a current output controller such a “homemade” device will not be able to crank the engine, but is guaranteed to fail itself.
Real ways to start with a dead battery
If the stock battery is completely discharged, there are proven and safe methods for starting the engine that do not require the use of a power tool battery. The first and most reliable way is to “light it” from another car, observing the correct sequence of connecting the wires.
The second option is to use a special booster, which was mentioned above. This device should be charged in advance and stored in the glove compartment. The third method is only suitable for cars with a manual transmission - push start.
- 🚗 Lighting up: Connect the wires to the donor and recipient strictly according to the instructions (plus to plus, minus to ground).
- 🔋 Booster: Connecting a compact lithium device to the battery terminals.
- 🏃 From the pusher: Accelerating a car in gear to turn the crankshaft through the transmission.
- 🔌 Charger: Connect a stationary charger to a 220V network for 15-30 minutes for a surface charge.
Each of these methods has its limitations. For example, for push start on fuel-injected cars, a minimum residual voltage in the on-board network may be required to operate the fuel pump and ECU (electronic control unit).
☑️ Check before launch
Risks and consequences of incorrect connection
Ignoring electrical safety rules when experimenting with batteries can lead to serious consequences. Lithium batteries used in screwdrivers are very sensitive to short circuits. When you try to remove a current from them that is 5-10 times higher than the rated current, the elements suddenly heat up.
In the best case, the BMS protection will work, and the battery will have to be taken to a service center to reset the error or replace the fuse. In the worst case, thermal runaway leading to electrolyte ignition and open fire. This is especially dangerous in a confined space in a garage or in a car in winter.
⚠️ Warning: Never try to connect batteries of different types (acid and lithium) or different voltages without an appropriate converter.
There is also a risk of damage to the vehicle's electronics. Voltage surges or incorrect polarity can damage expensive control units such as ECU, immobilizer or multimedia system. Repairing such components will cost much more than purchasing a new car battery.
How to properly store and maintain batteries
So that the situation with a discharged battery does not take you by surprise, it is important to follow the rules for operating power supplies. It is critical for car batteries to maintain a charge during the winter. If the car is parked outside, it is recommended to remove the battery and bring it into a warm place or use automatic chargers with storage mode.
Screwdriver batteries also require maintenance. Lithium-ion cells cannot be stored completely discharged, as this leads to irreversible degradation of the cell chemistry. The optimal charge level for long-term storage is 40-60%.
The secret to extending the life of Li-Ion
Do not store batteries in the cold. Low temperatures increase internal resistance and can cause deposits to form on the electrodes, reducing current output.
Regularly checking the contacts and cleaning the terminals from oxides helps to avoid loss of current and starting problems. Use special terminal lubricants to prevent corrosion.
FAQ: Frequently asked questions
Is it possible to charge a car battery by charging a screwdriver?
No, that's impossible. Chargers for screwdrivers have a voltage of 18-20V and a specific charging algorithm that is incompatible with lead-acid car batteries. An attempt to charge a car battery with such a charge will lead to its combustion or boiling of the electrolyte.
Will BMS protection work if you connect a 18V battery to a 12V on-board network?
Most likely yes. Although the voltage of 18V is higher than 12V, the current that the car's circuit will try to draw (especially when turning on the headlights or the radio) can exceed the limits of the tool's battery. In addition, the BMS may regard the connection to the external network as a fault and block the output.
What is the minimum current needed to start a 1.6 injection engine?
To reliably start a 1.6-liter gasoline engine in the summer, a starting current of at least 200-250 Amperes is required. In winter, this figure increases to 300-400 Amperes due to thickened oil and decreased chemical activity of the battery.
Why can't lithium batteries be used as permanent starter batteries?
Although lithium starter batteries (LiFePO4) are available, conventional tool batteries are not suitable due to the lack of a heating system and the inability to withstand vibrations and temperature changes in the engine compartment. Specialized lithium batteries are much more expensive than lead batteries.
Expert tip: Always keep a set of quality jumper leads with a copper cross-section of at least 16 mm² in your car. Thin wires made in China may melt the first time you use them.
In conclusion, it is worth noting that technological progress does not stand still, and perhaps universal modular power systems will appear in the future. However, at the moment, attempting to use a screwdriver battery to start a car is technically illiterate and potentially dangerous. Take care of your equipment and use only the energy sources intended for it.