The symptom pattern

The battery’s in, the lock key looks fitted, and pulling the handle lever does precisely nothing. It’s an easy moment to assume the mower itself has failed — but the DLM380 is built with several separate things that all have to be true before it will run, and on a cordless mower most “won’t start” reports turn out to be one of those, not a fault at all.

What’s actually happening

Makita’s own troubleshooting table for this mower lists “mower does not start” with two causes, in this order: two battery cartridges not installed, and battery undervoltage. The DLM380 is a 36V tool built from two 18V LXT packs — fit only one, and by design it won’t run.

The lock key matters just as much. It’s a physical interlock: fit it into the switch, close the battery cover, and the tool’s electronics complete. Leave it out and the mower won’t so much as attempt to start, regardless of how good the batteries are.

The part that catches most owners out, though, isn’t in the fault table at all — it’s in the mower’s normal operating instructions. Makita state it directly: “the mower does not start without pressing the switch button even if the switch lever is pulled.” The DLM380 has both a switch button and a switch lever on the handle, and they have to be operated in that order — button first, lever second, held together. Pulling the lever on its own, which is the instinctive thing to do, achieves nothing on this mower.

Working through it

Start with what’s fastest to check and rule out in order. Confirm two batteries are fitted, both showing charge on their own indicator. Confirm the lock key is in the interlock switch and the battery cover is properly closed. Then check the start sequence itself: press the switch button with one hand, and only then pull the switch lever toward the handle while still holding the button — not before it, not instead of it.

If all three of those check out and the mower still won’t run, recharge both battery cartridges fully before trying again; Makita name undervoltage as the specific cause behind this exact fault. If a full recharge on the charger doesn’t bring it back, that pack has reached the end of its useful life rather than developed a fault as such — it needs replacing, not repairing.

The one case to stop for rather than keep troubleshooting is the switch itself. Makita’s manual carries an explicit warning before you ever fit a battery: always check the switch lever actuates properly and returns to its original position when released, because a switch that doesn’t do that correctly is a loss-of-control risk, not a nuisance fault. If the interlock switch or handle switch feels wrong in any way — doesn’t click home, doesn’t spring back, or the mower starts without both the button and the lever being used together — Makita’s instruction is to stop operating it and have it checked by an authorised service centre. There’s no owner-level test or replacement procedure given for either switch, and this isn’t the part of a mower worth working around.

Verdict

Free, in order: batteries fitted and charged, lock key in, button-then-lever. That clears the large majority of “won’t start” reports on this mower without spending anything. A pack that won’t hold charge after a full recharge is a normal replacement, priced like any 18V LXT battery. A switch that doesn’t actuate correctly is the only genuine fault here, and it’s a service-centre job by Makita’s own instruction — not something to test by running the mower anyway to see what happens.