Quick answer
A common reason a Ryobi 40V mower won't start with a charged battery is an interlock problem, not a motor problem. Check these in order: handle fully extended and cam-locked, start key inserted, battery clicked all the way home, then the bail-bar-plus-button sequence done in the right order. If all that's correct, suspect a pack that reads full but sags under load.
The symptom
You charged the battery, the gauge shows full, you squeeze the bail bar and push the start button, and nothing happens. No beep, no click, no half-hearted blade spin. It's June, the grass is a week past due, and the mower is a paperweight. Before you load it in the truck for a service center visit, run through the list below. Most of these take under a minute to check.
Try this first: the handle
On Ryobi 40V mowers (for example the RY401110, and the RY401017 mower sold in the RY401170 kit), the handle is part of the safety circuit. If the telescoping handle isn't fully extended with both side cam levers clamped tight, the mower will not start no matter what else you do. This is the single most common cause, and it bites people who stow the handle to store the mower vertically and then don't quite re-seat it.
Pull the handle out to full extension, snap both levers closed hard, and try again.
Then the interlocks
- Start key. The start key must be pushed fully in, as your manual shows. A key that's partly seated can look fine and do nothing.
- Battery seating. Slide the pack out and back in until it clicks. A pack resting on the rails without latching will show a full gauge and still cut out. While you're in there, brush any grass clippings or corrosion off the contacts with a dry cloth.
- Sequence. Check your manual; on the manual I found, you press and hold the start button, then engage the bail. Releasing the bail stops the motor, which is how it's designed to work.
The battery that lies
A 40V pack can show four bars on the fuel gauge and still be the problem. Voltage at rest is easy; voltage under the load of a 20-inch blade is the real test. A worn pack can show charge on the gauge and still fail the moment the motor pulls real current, so the mower either won't start or starts and dies in a second.
The clean diagnostic: put the suspect pack in another 40V tool under load (a blower or string trimmer works), or borrow a known-good 40V pack and try the mower. If a second battery starts the mower, you've found it. Replace the pack, and remember Ryobi's 18V ONE+ batteries don't fit 40V tools, so the spare has to be from the 40V platform.
One cold-weather footnote that confuses people in shoulder seasons: a Li-ion pack won't charge when it's too cold, and Ryobi's charger indicator lights show when the pack is too hot or too cold to charge. That's a normal protection interlock, not a dead charger or battery.
Heat, clogs, and the reset
If the mower died mid-mow in tall or wet grass and now won't restart, you're probably in thermal protection. Pull the battery and the key, tip the mower on its side, and clear the packed clippings out of the deck; a clogged deck is a constant overload. Give the pack and the mower time in the shade until they are no longer hot, then try again.
When it's the hardware, not you
If a known-good battery, correct handle position, and clean interlocks still get you silence, the possible failures include the start switch, the bail-bar switch, or the motor controller. At that point it's a parts-and-labor decision: check whether your mower is still inside Ryobi's warranty window before paying a service center, and register the tool if you never did.
The honest summary: start with the handle, trust the bail-bar sequence, and never trust a fuel gauge until the pack has proven itself under load.