Argh… since I updated to 10.11.4 my Apple bluetooth mouse is disconnecting every now and then. They said they had fixed bluetooth issues, but for me they just started …
I had this happen on my 2011 iMac since at least Mavericks. Never found any remedy. I wonder if this would be due electromagnetic to interferences.
The list of possible causes on the Apple site is impressive https://support.apple.com/en-us/HT201542
I cannot live in an aluminium foil cage, though.
happened ever since I got my magic mouse
no idea why
wires are a pain… but only time I’ve had a problem with a wired mouse is when finally just wore out… then $9.95 for a new one. Never had luck with bluetooth mice or keyboards… sucked up batteries, lost pairing… decreased productivity
I just taped an aluminum sheet under my desk. Hope this extra shielding will help.
On the PC I have an Apple corded mouse, but I can’t really abandon the gorgeous form factor of the Magic Mouse on the iMac.
If apple made a wired magic mouse I’d be all over it and buy several
I had thought the wired and bluetooth Apple mice were the same (except for the interface of course)… But I just checked the store, and the Magic Mouse is a totally different shape… Where the heck are the button(s)?! I need tactile feedback 
Plus it doesn’t feel “comfortable” to me. but then neither does the Apple wired mouse… and don’t EVEN ask about that pea sized trackball.
Right now I have a $9.95 Dynex (BestBuy) mouse on my iMac… fits nicely in my hand. has a track-wheel/button,as well as acting as a proper “two-button” mouse. (none of that ctrl-click stuff).
I have a drawer full of the Apple wired mice and a trackpad that came with various Macs over the years.
I am using the logitech performance mouse mx because i hate the apple mouse 
High recommended if you want nice feel in your hand and no problems…
I using it more than 5 years and this is the new one i buy it before 2 days…
Battery hold, until message come up for low battery more than 42 hours…
If anyone want i have 4 apple mouse i give it free
The Magic Mouse is a sort of curved trackpad made into a mouse. It has a mechanical click left and right, and the wheel is replaced by a stroke (vertical and horizontal). I find that very precise, very endearing. And frankly having no cord is quite enjoyable with such a lightweight device (94 grams with batteries). I have know all kinds of mice through the years since the very first one, and still have drawers full, but I fell in love when I got it with the iMac.
That said, each one of us has his own preferences, and that is just me.
I have a logitech BT mouse with my MBP. No problem with El Capitan vs the mouse so far. It’s just one thing: while taking the stuff out of the backpack first switch on the mouse and then the laptop. This is important otherwise you end up peeling with the BT settimgs.
I could not manage to get my BT headset connected.
The solution was to upgrade mine with one that uses a USB CABLE… Works every time and I don’t have to charge batteries for it or anything.
Now if only the trackpad would have a wired option.
For ergonomics it’s best to place your mouse in front of the keyboard(not to the left or right) and that makes a wired mouse a no go
I don’t have a source on why the mouse should be between you and your keyboard. There was an ergonomics guy here at work observing our positions, and that’s what he said.
Try it, feels great and less train on your shoulder and neck.
This happened with me. What appeared to work was not using rechargeable batteries and get some high powered batteries 2000mAH.
Yes, try using other batteries. Previously I used 1200mAh, now 2100mAh and never have issues.
Bashing OS X again? 
I see this on both OS, since Windows/OS X supporting BT HID connections. With MS, Apple and Logitech Hardware…
[quote=255189:@Sascha S]Bashing OS X again? 
I see this on both OS, since Windows/OS X supporting BT HID connections. With MS, Apple and Logitech Hardware…[/quote]
Not just OS X, everything I have that has Bluetooth, has failures at some point. Even the Sony PS4 with Bluetooth controllers, can be unreliable, such as not responding or sometimes needing to be within 5 feet of the console. There’s nothing like hurtling towards a wall at 200 mph, and to lose control of your car!
Bluetooth file transfer with older phones was always hit and miss, Bluetooth keyboards on iOS simply refuse to connect sometimes and requires restarting both devices.
I personally have almost given up with BT input devices on my 2012 MBP and used wired ones. Yeah I have ugly cables, but they work all the time (until I’ve worn out the microswitches).
Got eaten by 2 Zombies yesterday because my PS4 Controller was suddenly offline. 
Same, except Magic Mouse 2 and Magic Trackpad 1. But just because there are no real wired replacements. 
I resolved problems with an old magic mouse randomly disconnecting by cleaning the power switch on the base. Lint had built up and the switch was only just making contact. Occasionally the power would toggle off and on as I moved it.
Worth a look.
[quote=255203:@Sam Rowlands]There’s nothing like hurtling towards a wall at 200 mph, and to lose control of your car!
[/quote]
Doing it in real life
It was only 196 mph (loved that car!)
I did get control before the wall - hence I’m here to say “what an idiot I was”
When my mother-in-law wanted a keyboard to use with her iPad, rather than deal with Bluetooth I set her up with a USB keyboard connected to the iPad using the camera connection kit. Completely reliable and I never have to worry about trying to explain Bluetooth pairing to her.