I accidently hit a rock with my WorX cordless mower and now it will only run for a few seconds before shutting down. The blade seems to still be in balance. I don't know what to do from here, any thoughts?

Mulch plugs are typically a cover that is affixed to the discharge chute of a mower deck. As blades spin, they cut grass, and lift them up into the swirling air above the cut grass and below the mower deck. The clippings are suspended until they are blown out of the chute.

Mulching, is the process where grass clippings aren't simply discharged out of the chute after cutting; rather they are kept under the mower deck and spin around suspended in the blades resulting in repeatedly being cut. Instead of long clippings exiting the chute, much smaller clipping result from multiple cuttings and settle back on to the lawn under the deck. The smaller clipping allows them to decompose much quicker and return nutrients to the lawn.

Long clippings take longer to decompose and can turn into thatch on top of soil between blades of grass - effectively smothering the lawn. Long clippings can sit on top of cut grass and choke off sunlight, etc. and cause dead spots. Thatch can occur with mulching too - but takes longer to accumulate.

I nearly always mulch

I think the motor brushes are warn out and need replacing.

WORX Lawnmowers seem to be incredibly unreliable, at least according to their own customer reviews. I found that Sears (one of their retailers) does carry some replacement parts, including motors, but often the models are updated, and beyond their 2 or 3 year warranty, the motors are discontinued. You may have to look for another WORX mower being sold for parts to acquire a working motor. Alternatively, keep checking EBay for a used motor. When operational, the WORX mowers are great, but with only a 2 to 3 year life expectancy, they are not the bargain they appear to be at first. Many customer reviews give high marks for the first year. Fewer for the second year, and by the third year, you'll be hard pressed to find a positive review of their mower products. I'm a WG780 owner: 2 years and my mower was shot too. WORX will not offer replacement motors, and will not offer repair service beyond their 2 or 3 year warranty (Two year warranty for machines sold prior to 2013; three year warranty after 2013) . Their operators will tell you that you'll need a new mower. Service during the warranty / Nothing afterwards.

The batteries are defective in this unit. It should be returned to the dealer that you purchased it from and get exchanged, or your money back. Another way to test this mower is to charge the batteries fully, then test them. If they are truly fully charged, run the mower until it slows down, and test the batteries again. If they are still charged, (unlikely) then the problem is in the motor itself and still should be returned.

Remove the deck and check the blades and spindles. I suspect your issue is electrical and not mechanical though.

did you hit a rock and bend a blade

This happens often. Sometimes your mower will start and run again and sometimes it won't. When it doesn't run it's because your timing is off, caused by a dented or sheared key.
To replace remove top cover to engine, and any other side attachments, this should expose the flywheel. Remove the top bolt and look between flywheel and top of crankshaft, you will see a small square notch. This is where the shear key is placed. Remove the flywheel and replace the shear key. Replace all parts in reverse order and you should be mowing again. GOOD LUCK.

The first thing I would do is to look under the deck and see if the blade is hitting up against what I call a ring wall. This ring wall is in almost all mowers wether electric or gas. I believe it,s designed to keep the cut grass from clumping up under the deck and not discharging out the shoot. Sometimes grass, twigs, rocks, etc. get caught behind this wall PUSHING the wall out towards the blade. The blade in turn starts hitting the wall making the sound you are hearing.
First removed any grass from behind the wall, second take a hammer and tap the wall back to were it should be. Rotate the blade buy hand to see if their is clearance, if so you should be ready to mow again. GOOD LUCK.

it could be a low lift blade on it. try to get gator blade for mulching..... or a high lift blade. lol, size does matter!!! this may fix the issue. there is so many blades out there now, experiment till you find what your looking 4......

If you hit something hard enough to partially shear the key on the blade adapter, you did shear the key on the flywheel, and it will need to be replaced for the engine to run properly.