18 V, 36 V, 40 V and 56 V mower batteries explained

Volts, amp hours and watt hours in plain terms

Volts (V) are the electrical pressure the pack supplies. Higher voltage lets a motor produce more power without drawing a huge current, which is why larger mowers and wide decks tend to sit on 36 V and above. Voltage on its own does not tell you how long the mower will run.

Amp hours (Ah) describe how much charge the pack stores. A 5 Ah pack holds more than a 2 Ah pack of the same voltage, so it runs longer, weighs more and takes longer to charge.

Watt hours (Wh) combine the two: volts multiplied by amp hours. This is the total energy in the pack and the figure that tracks run time best when you compare different systems. Some makers print Wh on the pack; if not, multiply it out yourself.

Why 36 V and 40 V packs can be the same thing

Lithium-ion cells have a nominal voltage of about 3.6 V and reach about 4.2 V when fully charged. A pack of ten cells in series is therefore around 36 V nominal and around 42 V at full charge. Some makers label that pack 36 V and others call it 40 V, sometimes with the word max. The same applies lower down: 18 V packs are sold as 20 V max in some markets.

So a 36 V mower and a 40 V mower are not far apart on voltage. Compare the deck width, the Ah of the pack supplied and the stated lawn area instead. The maker's manual or website will say which nominal voltage applies to your pack.

Twin 18 V mowers: two packs working together

Several brands run their larger mowers from two 18 V packs at once, wired in series to give 36 V. Makita's DLM462 and Bosch's UniversalRotak 2x18V-37 are examples in our guides. The appeal is that you can use the same 18 V packs in a drill, a strimmer or a hedge trimmer.

The catch is that you need two charged packs for every mowing session, and both should be of similar capacity and condition. If one pack is older or weaker, the mower usually stops when that pack runs low. Check the manual for the maker's advice on mixing pack sizes.

• Good fit if you already own several 18 V packs from the same brand.
• Needs two packs per session, so a twin charger or spare pair helps on bigger lawns.
• Single 18 V mowers, such as compact 33 cm models, suit small lawns and light growth.

What each voltage tier usually means for your lawn

These are broad patterns rather than rules, because deck width, motor design and grass conditions all change run time. Use the stated lawn area on the listing as your guide, and measure your lawn with our lawn area calculator before you buy.

Compare cordless mowers by battery and deck →

Why the platform matters more than the number

Batteries are the expensive part of a cordless kit, and packs only fit tools from the same maker and the same voltage family. Ryobi ONE+ 18 V packs fit Ryobi ONE+ tools; EGO 56 V packs fit EGO 56 V tools; Greenworks runs separate 24 V, 40 V, 48 V and 60 V families. Once you own two or three packs, switching brand gets costly.

Before you buy, list the other tools you want: a strimmer, a hedge trimmer, a leaf blower. Pick a platform that covers them. If you want a mower and strimmer on one battery from the start, our mower and strimmer set guide groups kits that share a pack. For lawns over a few hundred square metres, see cordless mowers for large gardens.

1. 1

   Measure your lawn area in square metres.

2. 2

   Check the stated lawn area on the mower listing and allow some margin for long or damp grass.

3. 3

   Work out the Wh of the pack supplied (V x Ah).

4. 4

   List the other cordless tools you want on the same battery.

5. 5

   Choose the platform that covers your lawn and those tools.

Note:Lithium batteries: use only the maker's charger for your pack, do not charge or use a pack that is swollen, cracked, leaking or has been dropped hard, and store packs away from heat, direct sun and frost. Take worn or damaged batteries to a proper battery recycling point, never household waste.

Frequently asked questions

Is a 40 V mower more powerful than a 36 V mower? Not necessarily. Many 40 V packs are the same ten cell design as 36 V packs, labelled by their peak rather than nominal voltage. Compare deck width, Ah and the stated lawn area instead.

Can I use a higher Ah battery in my mower? Usually yes, if it is the same maker and voltage family and the manual lists it as compatible. A bigger pack runs longer but adds weight. Check your manual for the approved packs. For more on run time, read how long a cordless mower battery lasts.

Can I use another brand's battery with an adaptor? Third party adaptors exist, but they are not approved by the mower makers and can void the warranty or bypass protection circuits. Stick to the maker's own packs and charger.

Why does my mower slow down before the battery is flat? Many mowers reduce power or cut out to protect the pack when voltage drops or temperature rises, especially in long or wet grass. If a pack will not charge afterwards, see our guide to a cordless mower battery not charging.