That faithful mower that has served you for several years now refuses to start when you turn the key, or press the start button.  Age, heat, and time have conspired to bring the battery to the end of its useful life. The battery needs replacing but the yard also needs attention.  This situation raises the question, “Can a lawnmower run without the battery?”

The lawnmower will continue to run without the battery. Most small gasoline engines use a magneto built into the engine to provide the electricity to create the spark in the sparkplug.  Provided you can spin the engine using a rope starter, or by boosting the dead battery to spin the engine, the engine should start and run.

You can, in all probability, get your lawnmower started quickly enough and it will continue to run.

However, you may still face diagnosing the problem that led to the dead battery in the first place.

There are also some dangers to operating some electrically started lawnmowers without the battery attached or with a dead battery.  Let’s take a look at running a lawnmower without a battery.

Is it Safe to Run your Lawnmower Without the Battery?

In short, it depends.  You won’t harm the engine by running it without the battery attached.  If you can get it started, it should run on the magneto driven spark.

However, if you leave a damaged battery attached to the charging system or run the engine without a battery attached, it can damage the control systems on the charging system.

Some charging system controls sense the condition of the battery.  A battery that is damaged and won’t take charge or a missing battery will cause the control unit to work at maximum output all the time.  The electronic components in these control units are not meant to operate continuously at such high output and will eventually fail.

Operating at the maximum output leads to more costly repairs than replacing a bad battery.

Getting your Lawnmower Started Without a Battery

Electrically started lawnmowers can be a challenge to get started if the battery is dead or missing.  The processes for starting a lawnmower with an electric start that is not functioning depends on the size and design of the lawnmower engine.

• Small Engines – Most walk behind and some smaller ride-on lawnmowers will have the traditionally recoil pull rope starting mechanism as well as the electric start. Follow the manufacturer’s instructions on preparing the engine to start and pull the rope.  Starting the engine in this situation is just like starting an engine without electric assist.

• Larger Engines – Larger ride-on lawnmowers and garden tractors often do not have manual start equipment installed due to the higher compression on the larger engines. It is next to impossible to pull-start these bigger engines.  In these instances, you must resort to either installing a new battery or jump-starting the engine with a jump start battery.

If you must jump-start your larger ride-on lawnmower or garden tractor, you should follow some basic rules.

• Be Safe – Wear your eye protection and gloves.
• Follow the manufacturer’s recommendations – More than likely, the user manual provided with your equipment will have specific recommendations on how to jump-start your engine.
• Make sure the voltages match – Don’t try to use a 12 volts jump-starter on a 6-volt system. You can damage the electronics.

Understanding your Lawnmower Engine

Electrically started lawnmowers typically have two distinct electrical systems.  One of these systems creates the spark that keeps the engine running and the other recharges the battery and keeps it in good working order.

Magnetos

Your lawnmower uses a magneto to generate the spark that fires the sparkplug to make the engine work. Magnetos are extremely simple and remarkably reliable.  There are only a few parts that you need to understand.

• The magnets – Several magnets embedded in the flywheel of the engine are the driving force in the magneto operation. The magnets in the flywheel spin past the armature mounted on the engine, which generates the spark.

• The armature – The armature is a transformer that collects the electricity induced by the magnets on the flywheel. The coils in the armature boost the amount of electricity enough to create the spark in the sparkplug

• The control unit – The magneto needs a simple control unit that controls how the electricity is boosted to the correct level to make the sparkplug spark. The control unit may also manage the timing of the spark.  On new mowers, this happens electronically.  On older mowers, a coil and breaker points manage the job.

Magnetos are incredibly reliable, and it is rare to find a problem with the actual magnets and armature themselves.

The electronic controls can fail, which will prevent your lawnmower from starting and running or may cause intermittent problems that can be hard to diagnose.

The Other Side of the Electrical Issue

On the other side of the electrical issue with lawnmowers is the charging system that keeps the starting battery charged and to operate any auxiliary systems such as lights, gauges, etc.  There are two variations on charging systems.

One operates from the same magneto that provides the spark to the sparkplug and the other uses a small generator driven by the engine to provide the electricity.

• Magneto driven charging systems – The charging system on your lawnmower may draw its electrical power from the same magneto that provided the spark to the engine. This electricity generated by the magneto passes through a module called a rectifier that converts the AC electricity into DC that charges the battery.

• Generator driven charging systems – On larger mowers and garden tractors, the engine may have a separate generator or alternator driven by the engine that produces AC or DC that charges the battery and operates other equipment on the lawnmower.

Both systems depend on electronic control devices that can convert the AC output to DC that is compatible with the 12 or 6 volt electrical systems found on most lawnmowers.

These control systems not only manage the conversion of the AC to DC, but monitor the voltages and, in some cases, the condition and the charge level of the battery to prevent the charging system from overcharging the battery.

Maintenance is the Key

Rather than find yourself in the situation of having to run your lawnmower without the battery, a bit of regular maintenance can prevent you from facing this situation.

Spending a few minutes each time you use the lawnmower as well as at the beginning and end of the season can prevent a lot of problems. These tips can help keep the electrical system on your lawnmower in top shape.

• Check all the wires and cables before each use. Repair or replace frayed or damaged wires, including the sparkplug wires.
• Check the battery for cracks or other damage to the battery itself.
• Check the battery connections and remove any corrosion. Tighten the battery connections if the wires have clamps.
• Use a voltmeter to check the output of the magneto or generator. The user manual should specify the voltages that the system should produce.
• Check the charged voltage of the battery to ensure that the battery is holding the proper charge.
• Check the sparkplug, clean, and reset the gap if necessary.

Making the Cut

Keeping that lawnmower running is the key to making your landscape maintenance less of a chore.  If necessary, you can run that lawnmower without the battery in most instances.

Running your lawnmower without the battery is, of course, not the ideal situation.  You should root out the cause of the problem and make the necessary repairs to keep an expensive piece of equipment operating correctly.