Just rediscovered after 10 years but minus charger and headphones...

If the bluetooth you are referring to is a bluetooth earbud, the batteries may be dead. You may need to buy a new earbud.

There are lots of universal battery chargers, that can detect what voltage your battery is and what is plus and what is minus.
I use one for all my camera's. The only thing I have to do is turn the contacts in the right position. But there are new ones, that find out where they have to put the voltage.
Most of the time the universal chargers are cheaper and you can use it for more than just that one camera.

Same problem with my 780 and have had no luck with a genuine charger and Dremel have discontinued it. I resorted to using a 10volt charger bought online and connected the the two wires to the battery terminal. + to Plus and - to minus. A bit dodgy I know but you can't get a wallop out of 10 volts, just keep and eye on it in case you start a fire! (very unlikely ). Feel the battery every now and then and when it gets a little warm, turn the charger off and make good use of the Dremel. I know this is not perfect solution, but the only alternative is give up on a perfectly good tool or buy the whole kit second hand (drill box and pieces etc).

Just search google shopping for your battery, or ebay, just make sure you read the details, and choose wisely so you don't get scammed off ebay. I buy a lot of stuff off there with most all being good purchases, but there are scammer's everywhere anymore.

its just 3 things.
1; battery
2: charge regulator on the device.
3: power pack
one is bad.
so its not battery, now its #2 or #3

seen the regulator is toasted
very common
why not buy as used spark same device, and mix part to get good
or ditch it and upgrade,

you should try to clean out the headphone jack, and the charger part on the bottom
try going to an office supply store like staples or office depot, and buy a can of computer duster, it is compressed air which really helps to get the stuff out
another thing to do is to hold the home and lock button at the same time for about 10 seconds until you see the apple icon, then release and it should be back to normal

My Sennheiser HDR 140 headphones charge whenever you hang them on the charger. The charger will "trickle" charge them to keep the batteries fully charged. If you find when you use it the batteries discharge quickly it's time to replace them.
My batteries are about 2 years old and I still get about 8-10 hrs of use before needing to recharge

I think if you have a battery that is pretty much dead, the Makita charger will never fully charge it and so it blinks. My newer battery charged up in 1/2 an hour but my old-as-the-hills one just keeps on blinking. I removed it and it works. It never really held a charge long though, for years now. It would be nice if the charger had some kind of manual telling you what all those universal symbols(I don't know who's universe they're talking about) mean.

If you have an account on ebay.com,you can purchase it online. so goto www.ebay.com thanks

Dance_to_it -
I have had these great headphones over 15 years (I think!)
1. Are the batteries getting a full 8 hour charge?
2. Have you tried all 3 channel options?
3. Is there anything else close by that is an RF transmitter or receiver? If so, move the headphone base or other RF instrument away from each other.
4. If these are the original batteries you probably need new ones.
5. When purchasing new batteries I recommend original equipment Sennheiser BA151 batteries, not any other brand. I have tried 3 or 4 other brands, all with less than satisfying results. I have no affiliation with Sennheiser corp., just a consumer of their products (and Grado's for wired headphones)
Good luck!
-KWS