Ryobi Multi tool RMT1801, has a broken battery contact. I can get sides apart, but can not get the top (head) part off, any ideas?

Question edited for clarity.
Question moved from Cars and Trucks.

Difficult without a Letter/Numerical Model Number, but this seems to indicated it has a left hand thread, which means it turns clockwise to undo. That was my first thought, so I looked for a manual.

https://images-eu.ssl-images-amazon.com/images/I/B1X7J5EPy4S.pdf

The search query should be 'make model manual'.
https://www.google.com/search?q=ryobi+multi+tool+manual

..

Do you mean the Ryobi 40V X-head cordless string trimmer? This model has a 12-15" cutting width. For the 40V battery, you remove it by pressing and holding the latch button at the bottom of the battery (on the side closest to you). Then pull the battery out of the power head, exactly reversing how you slid it into place. Do not release the latch button until the battery slide free of the tool. The latch is usually stiff and takes a lot of force to hold down. See Fig 4 for the position of the latch in the manual: https://images.homedepot-static.com/catalog/pdfimages/fa/fab7f50b-d65b-40de-9e1c-5fecce2436f5.pdf . The same directions apply to removing the battery from the Ryobi 40V string trimmer with the fixed head.

For the 18V batteries, there are two latches, one on each side of the battery. Press and hold again. These are so stiff that my mother and I often need someone else take off the battery from any of the Ryobi tools. (We're both about 5' tall and 100 pounds. The tools aren't designed for our proportions.)

I hope this helps.

Cindy Wells

Is the machine turning on?
Is the motor / transformer going but the head not?
I can only ASSUME that they are.
Pull it apart and you will probably find that a cam, sprocket or pin of some sort is broken. Some machines use a oscillating transformer action. This coil may be open circuit. A multi-meter check will soon tell you. If this is the case then it is probably cheaper to buy a new or second hand one.

Check brushes in the drill.j

It appears that the recoil spring has broken and you will have to pull it apart to replace it

After 8 years its possible you have some corrosion or bad contact on drill, takeing it apart an checking inside may be to much for you,but make sure all contact are clean on outside.

This applies to Li-ion. NiCd is probably somewhat different.

Unscrew four security screws on the bottom of the battery. If you don't have the right bit you can grind down the center pins in the screw heads and use a T15 bit.

Unscrew the hex-head screw in the center of the protruding post at the top of the battery. It may be non-standard in size but a small metric hex key wrench works if you are gentle. The four corners of the battery cover should be loose now.

There are still two plastic clips holding the top cover to the main unit near the centers of the long dimensions. Gently push a knife blade into the crack between bottom and top to release the clip on each side.

As you lift the top cover off you should push down on the contacts near the top of the post so you don't pull on the attaching wires. Eventually the contacts should pop free and the top cover detaches.

Detach the wiring harness for the status LED from the circuit board. You can now remove the combined circuit board and battery pack from the lower case.

Six screws attach the circuit board to the battery assembly, along with several solder connections, but you probably don't need to go this far. You can now test and possibly replace individual cells.

The flex shaft drive you are referring to is only sold as a assy that I am aware of. You can try www.partstree.com for the replacement shaft assy. you are refering to, however you may find out by the time you buy a new shaft assy you may be money ahead just buying a new trimmer.
Sorry

Just got a reply from Ryobi tech service and it says that "all Ryobi 18V platform power tools can accept and use the lithium batterys, but you must use the charger for the lithium to recharge them. Hope this helps. Dave