Can I Jump Start a Lawnmower With a Car

A flat battery must be the most common riding mower complaint. It's so annoying to hear the click, click, click. Let's get it figured out right now!

So, can you jump-start a riding mower with a car? You can jump-start a riding mower with a car. Most mowers operate a 12-volt system. Put the jumpers on in sequences 1, 2, 3, 4, and start your mower. With the mower running, remove the jumpers in reverse order 4, 3, 2, and 1.

Not sure you have a 12-volt system – check the battery details on your mower. A sticker or stamp on the casing of the battery will indicate the voltage.

Common locations for batteries to be found – underhood, under-seat; under-drink holder, behind the wheel, and lots of other hard-to-find places.

Page Contents

Safety
Dirty Battery Terminals
Jumping / Boosting Your Mower
Connecting Jumpers
Tractor Battery Function
Battery Testing
What Battery Type
How Many Amp Battery?
Excessive Amp Draw
How To Charge Mower Battery
What Is A Smart Charger
Trickle Chargers
How Long to Charge Mower Battery?
Related Questions

Safety

Before attempting to jump-start, check that the battery is secure and not leaking. Leaking battery acid will burn your skin, so if the battery is wet, use gloves and eye protection. Check also that the terminals are secure and not damaged. Damaged or loose terminals will cause arcing and prevent the flow of power to the starter.

Dirty Battery Terminals

If your battery posts are dirty, clean them before jump-starting. First, kit yourself out with protective eyewear and gloves. It will look like a white crusty build-up on the terminals and battery posts.

Dirty, corroded, or lose terminals create a resistance to the flow of power from the battery to your starter, and in return, prevent the recharging of the battery by the alternator.

Sprinkle some baking soda on the terminals and add a small amount of water. This will neutralize the acid and remove the corrosion.

Use a wire brush to clean the surface. Now remove the terminals and clean around the poles and the terminals. Apply a coat of petroleum jelly to help protect against corrosion.

Cleaning The Battery Terminals

Battery terminals (connections) often come loose because of mower vibration, and as you know, corrosion is also common. If your battery terminals are damaged or badly corroded, replace them. Damaged cables may have broken wires within. This causes excessive resistance.

Often you may notice the cables getting very hot while you're attempting to start the mower. This is a sign of high resistance. Replace with good quality leads and terminals.

Cables – Damaged, worn or dirty cables will mimic a flat battery. Always check battery cables and terminals before condemning the battery.

Jumping / Boosting Your Mower

The jump/Boost start procedure is very simple; obviously, you'll need a set of booster cables. If you need to buy boosters, buy a good quality set. Poor quality cables won't make a good connection and make the whole job a lot more difficult.

I recently bought a set of Cartman boosters recently. I like cables that remain flexible in cold weather and jaw clamps that grip firmly, my guess is I'll have the years, but I'll keep you updated, and if I like them, I'll post a link on the "Small engine tools page."

Connecting Jumpers

Battery poles are sometimes colored red for positive and black for negative. However, batteries will definitely be marked (+) for positive and (-) for negative. You may need to clean the battery a little to find the markings.

Battery post markings – Look out for positive and negative markings on the battery casing.

Move your vehicle close to the mower and pop the hood to access the battery. You will likely have to remove a plastic shield from the car battery terminals.

Simply match the color and polarity of the leads. Always begin by fitting the Red (+) jump lead to both (+) battery poles first, but it's all covered below. Just follow the sequence, and you'll be mowing in jig time.

Jump Start Preparation & Jumper Sequence

A ground source is any bare metal. There's always a ton of good places on the engine to clamp to. Clamping the final clamp to the battery negative pole isn't advised. Doing so may cause arcing, which could ignite battery vapors. It's a small risk, but it is possible.

Check – All modern mowers run a 12-volt system, and it's perfectly OK to jump-start from your car. If you are unsure, check the battery casing, it will be marked 12 volts (V).

Tight – Mower blades and engines cause a lot of vibration, bolts come loose from time to time. Check both connections. Positive red (+) and negative black (-) are clean, tight, and in good condition.

Jumpers – Use good quality jump leads. These are my old worn-out ones.

Connect – Start by connecting the positive red (+) of the mower (1) to the red (+) of the car (2).

Now connect the negative black (-) on the car (3) to a ground (GRD) source on the mower (4). (Any bare metal will work)

Start – After starting the mower, allow it to run for a couple of minutes while still connected.

Remove the jumpers in reverse order, 4, 3, 2, and 1.

Mower Just Clicks

If you tried jump-starting your mower or the battery tested OK, then you may have a starter solenoid fault. These guys give lots of trouble, so it's highly likely, but it's not the only possible cause of the click sound. Check out this simple easy to follow guide, we'll test the solenoid, and I'll show you the other common causes of the click sound – "Won't start just clicks."

Mower Won't Start No Click

If you tried jump starting or the battery tested OK, but the mower makes no sound at all when you turn the key – You may simply have an open safety sensor, like not sitting on the seat or brake pedal not pressed, or you could have a more complex issue.

Anyway, I wrote a guide to help you find the problem. Check out all the most likely causes here "Mower won't start – no click."

Tractor Battery Function

The function of a lawn tractor battery is to start the engine. Once started, the alternator then produces the power required to run electrical systems and recharge the battery. Batteries are designed to give, receive and store electrical power.

A strong, healthy battery is critical to starting a lawn tractor mower. A mower engine only creates enough energy for the spark plug to fire if the engine cranks over fast enough, min 350rpm. So if your mower cranks but won't start, try jump-starting to eliminate the possibility of a faulty battery causing a slow crank speed.

Once the engines are running, a bad battery isn't so important. That's why a mower with a bad battery still runs after you remove the jumper leads. See crank testing the battery below.

Battery Testing

Checking for a full 12.65 volts on a battery at rest is fine for giving you an indication of the state of charge, but it's not a guarantee that it's OK. To test a battery for faults, it needs to be loaded, and by loaded, I mean worked hard.

100% charged is 12.7 – 13.2 volts
75% charged is 12.4 volts
50% charged is 12.2 volts
25% charged is 12.0 volts
Discharged (Flat) 0 – 11.9 volts

The fast and easy way to check the battery is to use a voltmeter set to 20 volts DC.

I've listed a voltmeter on the tools page. It's a good meter you'll have for years that won't break the bank "Small engine repair tools."

Battery Crank Test – To test a battery, it needs to be loaded with a voltmeter set to volts DC, red to red, and black to black. Have a helper crank over the engine. If the meter drops below 9 volts, the battery is faulty.

Charging System Test – If you have a voltmeter, checking your charging system is easy. With the engine running, set your meter to volts DC and connect the red to red and black to black. Any reading above 12.65 volts means your charging system is OK.

What Battery Type

There are many different types of batteries, wet, gel, AGM….. Let's keep this simple.

Don't buy a wet battery, you'll know a wet battery – it has fluid top-up plugs across the top of the battery. These batteries leak and usually all over the connectors causing corrosion. It needs to be topped up regularly and if you don't, you'll kill it and void the warranty.

They can't be stored indoors safely. Can't be shipped with acid, so if you buy it online, you'll have to go to an auto store and buy acid. Then using suitable gloves, eye protection, and a mask (because this stuff is nasty), fill the battery cells individually, careful not to overfill them.

Now you'll need to charge the battery, so you'll need a charger, back to the auto store……

Instead, buy a sealed battery, they're easy to handle, have no risk of leaks, no topping up of electrolyte needed, can be shipped and arrive locked and loaded. Check out the Amazon link below, for great deals on mower sealed batteries delivered to your door already charged and ready to roll.

Amazon Ride-on Tractor Mower Batteries Opens in a new tab.

12 Volt Battery

A typical lawn tractor battery is 12 volts. They are made up of six individual cells, each producing 2.10 volts. This makes a total of 12.65 volts when fully charged, however, referred to as a 12-volt battery. Within each cell are opposing lead plates of cathode and anode submerged in an electrolyte. The chemical reaction of these opposing lead plates causes electrons to flow – producing electricity.

Check Your Battery Shape

Batteries are classified by the shape, size, and orientation of posts and are given a group code, such as U1R this code will be marked on the battery. If you get this wrong the battery would still start the mower OK, but may not fit in its location or the leads may not reach the battery posts.

If you don't want to mess around with codes, just measure the battery height, width, and depth, note which side the posts are and if negative or positive. Go online and you'll be juiced up in no time.

How Many Amp Battery?

The bigger your mower engine, the more amps will be required to turn that engine over. The output of the battery is very important. When diagnosing electrical systems, and thinking about Volts, Amps, Resistance within that system and how all relate to each other, I find it helpful to think about energy as water in a garden hose.

Volts being the water pressure in the garden hose
Amps being the water flow rate from the garden hose
Resistance being the size of the garden hose

Amps

A single-cylinder lawn tractor starter motor will draw 80 – 100 Amps when starting the engine. The more mechanical resistance in the engine, the larger the draw.

For example, in cold weather when the engine oil is thicker, it's harder for the starter to turn the engine and so it draws more energy (amps).

Excessive Amp Draw

A starter pulling excessive amps will mimic a flat battery. The reasons a starter pulls excessive amps vary, common among them include:

Excessive valve lash
Hydro-locked engine
Faulty starter motor
Over full oil level
Oil too thick
Internal engine damage

Measuring amp draw is simple, however, you will need a clamp meter.

A typical lawn mower battery will be amp-rated and marked on a sticker 12 V – 32 Ah – 280 A.

12 v = 12 Volts
32 Ah = Means this battery can supply 1 Amp for 32 hours (1 Amp would be equivalent to a small light)
280 A = Max amount of Amps available

Other common reasons for a larger amp draw: worn starter motor; binding starter motor; engine damage; engine hydro-locked; overfull oil level; wrong oil type; valve lash off; failed compression release assembly.

How To Charge Mower Battery

To charge your riding mower battery, you will obviously need a battery charger. You don't need to remove the battery from the mower but you will need to remove the black negative (-) cable terminal connection.

Your mower may be fitted with a sealed maintenance-free battery or a regular lead-acid battery, both can be charged with a normal charger.

I prefer to use a smart charger, they're safe to leave on your mower all winter and can also be used as a normal battery charger.

Totally Flat Battery Charge Hack

If your battery is fully discharged, the battery charger will not charge it, it's designed that way. To hack this we need to fool the charger, simply connect the flat battery to a charged battery with jump leads in the normal way, then connect the charger and charge.

The jump leads and donor battery can be removed after an hour.

Wet Battery Charging

A regular lead-acid battery will have a fluid level indicator and removable cell caps as per the pictures below. A wet battery will need the cell caps removed and fluid level checked before charging.

Top up with distilled water or rainwater caught in a plastic container. Do not fill past max level. If you find any of the cells dry, then it's likely the battery is junk. Advise using protective eyewear and gloves.

Sealed Battery Charging

The sealed battery is much less work, you only need to remove the negative terminal before charging (don't need to disconnect if using a smart charger). You'll recognize a sealed battery, it won't have the fluid caps or fluid level indicator.

1 Volt – A fully charged 12 v battery reads 12.65volts. Any reading below 12.4 means the battery needs a charge.

2 Remove – Before charging the battery remove the negative terminal. No need to remove the positive terminal.

3 Fluid – If you have a regular lead-acid battery, you will have a fluid level mark. Check the level, it can be seen through the casing.

4 Top Up – Remove all plastic caps. Top up with distilled water or rainwater caught in a plastic container. Fill to the max. Use safety glasses and gloves, ACID WILL BURN CLOTHES AND SKIN

5 Sealed – You don't need to remove a battery to charge it, but sometimes removing it can be easier. A sealed battery is maintenance-free, just disconnect the negative wire and charge.

6 Charger – The charger is connected red to positive and black to negative, as per the picture. Charge time – about 2 hours.

What Is A Smart Charger

Consider buying a Smart/trickle charger, these chargers are connected to your mower when not in use. They put out a low amp charge of 1 to 3 amps which maintains your battery.

I treated my own tractor mower last year to a new smart charger, I bought the Noco Genius smart charger, you can check it out on the "Small engine tools page", I'm very happy with it so far, it's simple to use and works on all battery types, but I'll keep you posted.

Trickle Chargers

There are different types of trickle chargers:

Manual which needs to be turned on and off.
Smart auto charger – turn themselves on and off as the battery requires.
Hybrid version that will double as a high amp charger when needed.
Solar trickle versions are also available.

Using Trickle Charger

Connecting them is simple, pop on the color-coded crocodile clips and plug them in. This leaves you with a fully charged battery every time you turn the key. Batteries work best and last longer when their state of charge is maintained, off-season charging is always advised.

How Long to Charge Mower Battery?

This will depend on the size of the battery, how depleted that battery is, and the type of charger you using. There are fast chargers, trickle chargers, and smart chargers, all will vary in charge time. Usually, 3 to 4 hours is enough for most chargers to lift a flat battery.

Amp Rating

Chargers are amp-rated so, for example – the mower battery is a 32 amp-hour (Ah) and totally flat. Using a 10 amp charger to fully charge it, will take approximately 3 hours.

The Hybrid smart chargers are the best and of course, are more expensive, they are designed to charge and maintain your battery when the mower isn't in use. They will turn off and on as needed.