How Far Can You Drive with A Disconnected Battery?

It’s common knowledge that modern cars use a battery to start their engines. In contrast, a lesser-known fact is that later models also use the battery for other purposes.

When it comes to whether you can drive your car with a disconnected battery, the answer is simple: yes – at least in theory. In practice, it’s a different story. This article will tell you how many miles you can drive after disconnecting your battery. Also, we’ll show you why it’s something you should avoid. First things first – let’s discover the purpose of a battery in modern automobiles.

The Basic Function of A Car Battery

The most prominent role of a car battery is starting the engine. Using an electrical charge, the battery turns your engine’s crankshaft and lights up the spark plugs. As a result, the motor begins sucking fuel from the gas tank and lights it up. In other words, the engine starts running.The Basic Function of A Car Battery

After the car starts, it seems that the battery’s job is finished. After all, you have an alternator which provides all the electricity necessary to run your car’s lights, computers, air conditioning, etc. But is it as simple as that? Not at all. It might’ve been some 40 years ago, but today’s cars need a running battery to be able to operate safely. Don’t worry – we’ll explain why.

Learn More: How To Test Alternator By Disconnecting The Battery

The Battery’s Hidden Purpose

Most cars today use batteries with a 12-volt charge. That means that any electronics inside your vehicle will be made to work on that voltage. A lower voltage will not provide your electronics with enough juice. Likewise, a higher voltage carries with it the potential to fry your precious electronics. Your headlamps, air conditioning unit, even your ECU can take a lethal blow.The Hidden Purposes of car Battery

Apart from starting your engine, a car’s battery serves an additional function: it provides stable electricity to your car’s entire electrical system. Whereas the alternator provides a continuous power source, the battery evens the power out. By passing through the battery, your car gets a constant 12-volt current.

Should you disconnect the battery with the engine running, you risk the possibility of unleashing a massive amount of electricity at once. If such a thing happens, you can be sure that your car’s electronics will take a big hit.

Can I Drive With My Car Battery Disconnected?

As we said before – yes, you can. But should you? Absolutely not. Let us explain.

If you manage to start your car, it will continue running even after disconnecting the battery. That’s because car engines have alternators: compact generators can produce electricity by utilizing the engine’s moving parts. Therefore, once an engine starts running, it becomes self-sufficient – it no longer needs electricity to function.How Far Can You Drive With a Disconnected Battery

All of that being said, once it’s started, a car engine will continue running even without a battery. If you’re still wondering how many miles to drive after disconnecting the battery? the simple answer is: as many as your car can take you without running out of gas. However, the sensible thing would be never to disconnect the battery of a running engine.

If you still want to try driving without a battery, be warned: there is a risk of overcharging your electronics. Should this happen, it will likely ruin your engine. If you fry your ECU, the best you can hope for is paying a significant amount for a new one. However, since an ECU controls the inner working of your car’s engine, the potential for damage can be much more significant.

Therefore, prepare yourself to replace parts like the alternator, oil and water pumps, and possibly even pistons. A modern internal combustion engine is a high-strung piece of technology, and we wouldn’t want to mess with it.


The habit of disconnecting a running car’s battery comes from a long-gone age of motoring. In the past, cars would have carburetors instead of ECUs and roll-down windows instead of electrical ones. Today, it’s the opposite: nearly every aspect of your vehicle is electrically controlled, from how your engine runs to adjusting your seats.

Therefore, what would once mean only a couple of blown fuses, at worst, can completely ruin a modern vehicle.

Sure, in theory, you can cover great distances without a running battery, and, indeed, you sometimes have no other choice. However, we would never do it by choice: the possibilities of catastrophic failure are too great. Even if you manage to avoid severe damage to your car, you’re still likely to rack up a sizeable repair bill.

Hopefully, our article sheds some light on the function of a car battery and why you should never remove it. Take our advice: don’t play around with your battery, as it can cost you dearly.

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