Quick answer
Nine times out of ten a Ryobi 40V mower that won't start with a charged battery has 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 70-pound 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 (the RY401110 and RY401170-series 20-inch HP Brushless models are the common ones), 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. If the levers feel loose, tighten the handle bolts behind them.
Then the interlocks
- Start key. The flat plastic key under the battery cover must be pushed fully in. They work loose from vibration, and a key that's 90 percent seated looks fine and does 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. These mowers want the bail bar held against the handle first, then the start button pressed. Releasing the bail bar even briefly kills the circuit, which is exactly what it's designed to do.
- Grass catcher and discharge chute. A bag or side-discharge chute that isn't fully seated can hold the rear door open, and some models won't run with the door propped.
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. When one cell group inside the pack weakens, the gauge reads charged but the pack collapses 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 accept a charge below roughly 32F. 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 15 to 20 minutes in the shade, then try again. Mowers that have hit overload repeatedly may also need the battery pulled for a minute to reset the electronics.
When it's the hardware, not you
If a known-good battery, correct handle position, and clean interlocks still get you silence, the likely failures are the start switch, the bail-bar switch, or the main motor controller, in roughly that order of cost. 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. A controller replacement on an out-of-warranty mower often costs enough that the money is better put toward a current model.
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.