Magic Mouse (A1296) 14500 Rechargeable 3.7v Li-ion Conversion

UPDATE March 30: My Li-ion mouse lasted 29 full-time work days before (as expected) suddenly stopping due to protected li-ion cut-off. My net search WRT Eneloop MM users finds them reporting about 14 days of run-time (please add comment if that's off the mark). This still may not make this a rational, logical instructable to perform, especially if its preconditions (having li-ions & charger, "extra" MM, acceptance of risk) are not met.

Like these mice except for their consumption of AA (alkaline) batteries. No biggie for casually used machines but annoying for Macs used 40 hrs a week or more. Seems every 3 - 4 weeks, at inopportune times, I get low battery warning and have to grab new AAs & toss the old ones.

Researched Magic Mouse (MM) rechargeable battery solutions none seemed optimal usage-wise. They (all?) relied on NiMH batteries having nominal charge of 1.2v, so 2.4v combined. Seems fully charged NiMHs, even the excellent Eneloops, show 75% - 80% charge on mouse and only last a week [Edit: reports indicate closer to 2 weeks] of (heavy) use before needing recharge. Though the Mobee Inductive Charger looked like an interesting solution, it has the NiMH limitations & mixed reviews.

Having several spare good quality protected 14500 3.7v Li-ions, and a reliable charger for them, thought I could make better use of the spares. 14500s are nominally AA size (but protected ones are longer - see last step). If I could only somehow modify the MM to use them.

DISCLAIMER: THIS IS A DELICATE, TRICKY MOD. IT'S POSSIBLE YOU'LL END UP RUINING YOUR MOUSE IN THE PROCESS, RENDERING IT BROKEN. The tricky parts are mechanical ones (flexing plastic retainer hoops, re-attaching bottom metal + gliders), not electrical ones.

Notes:

• Don't yet know the long-term effects of running the mouse at higher voltages than it expects. But the one I modded has been working perfectly for days now.
• You'll be loosing the low battery warning since the protected Li-ion cell cut-off voltage is above that of the MM's warning voltage

Goal was to convert a MM to use two 3.7v 14500s in parallel. An unknown was whether MM circuitry would tolerate the higher Li-ion voltage (3.7v, 4v unloaded) than the series AA alkalines it was designed for (3v, 3.4v unloaded). It turns out it does, I've been using the modded mouse for days now & its working perfectly.

DISCLAIMER Redux: Think some skill, patience, luck and a crazy desire to pull it off are required. Helps if you've an "extra" or secondary Magic Mouse to try this on. And if you've protected 14500s & charger lying around so that they are not really part of the expense of this project.

What you'll need:

• Desire for long-lasting rechargeable MM has to outweigh the possibility that you won't succeed & will be sacrificing the MM to the cause.
• little prying devices (e.g. small flat-head screwdrivers),
• soldering iron w/somewhat fine tip, solder.
• slender tip needle-nose pliers,
• a couple short pieces of solid-core wire.
• any DMM to check connectivity.
• Dremel or small grinding tool + bit (to provide clearance for protected 14500 top/positive nubs).
• 4 high-quality, tested/reviewed protected 14500 Li-ion cells (2 for spares) and a reliable charger for them*. Need to be protected cells because mouse's low-battery cutoff is about 2.2v, too low / unsafe for 3.7v cells (protected cells cutoff @ about 2.7v or so).

* Do not buy or use any old/cheap/no-name cells or charger, only ones that are tested/reviewed - best reviews I've found are from "HKJ" on BudgetLightForum whose reviews are usually available here

The MM uses 3 volts by strapping its AAs in series - with a connection from left battery negative (lower left contact) to right battery positive (upper right contact) when viewed from bottom. You should confirm this with your DMM on ohms setting - should be at or near 0 ohms.

The plan is to break this series strap and make it parallel for your two 3.7v lithium ions by:

• desoldering / disconnecting right battery positive contact from PCB & attach the contact to left battery's positive terminal (when viewed from bottom - during the work this is reversed as you'll be viewing the PCB from its top!).
• strapping both batteries bottom / negative terminals together.

Disassembly: Others have documented MM disassembly fairly well here

and here

The key bits are:

DON'T ALLOW THE RIBBON CABLE AT MOUSE BOTTOM TO COME ALL THE WAY OUT OF ITS CONNECTOR. It's difficult to re-insert the cable. Always hold pressure to keep the lower portions of the mouse's upper & lower bodies close together. Check ribbon connector time to time during process & snug it back in using fine needle nose. And at end just prior to re-assembly.

DO YOUR BEST NOT TO BREAK THE FOUR PLASTIC HOOPS THAT HOLD THE MOUSE UPPER & LOWER PORTIONS TOGETHER. This is the most difficult part - flexing / prying 2 hoops on a side to free upper & lower mouse assemblies. If you break any you could try a bit of epoxy but don't get any within the loop holes or on the pins they engage.

Note: I did get minor splits in 2 of the 4 hoops yet the mouse still works perfectly. I think that as long as one upper & one lower hoop on opposing sides are somewhat sound the mouse should work properly.

You need not take out any screws from the mouse. Continually check that ribbon cable is still in its connector - use fine needle nose from time to time to snug it up & just before re-assembly.

1. De-solder / detach left side battery (as viewed from top) positive battery terminal from outer edge of PCB, its only attachment point.
2. Flatten the removed terminal, weave it behind the metal contact bar & solder jumper wire to right side battery positive terminal. Apply some epoxy / JB weld to center area under contact bar to secure relocated terminal, holding it close to battery compartment.
3. Run a jumper wire across lower / negative battery terminals.
4. Use your DMM to assure the bottom (negative) and top (positive) battery terminals are not shorted. They should read as open or some high resistance between them.
5. Assure that both bottom (negative) terminals are indeed shorted together & that both top (positive) terminals are as well.

You are ready for reassembly. Notes:

Use epoxy/JB weld to secure the new top/positive terminal, (glue) to re-attach the bottom metal portion of the mouse and to secure the 2 plastic gliders on each side of the battery compartment. The gliders have pins that I cut the tips off of to re-insert. This is an important tricky step - assure the gap around mouse top & bottom is fairly uniform, that the mouse pivots correctly (left- & right-button mouse presses work), and that the gliders are inserted such that mouse lies as flat as possible on a flat surface. I wrapped mouse in masking tape for a couple hours for epoxy to cure.

The mechanicals have to be fairly precise after re-assembly for the mouse to function properly. But even if your mouse ends up unusable you should at least come away with a greater appreciation of the engineering & assembly of the mouse.

As we are using protected 14500s and they are bit longer than AAs you'll need to use a dremel/grinding tool with small round cutter to enable them to fit. You need more clearance for cell top / positive terminal nubs, much of the mouse's battery top terminal plastic may need to be removed to assure contact.

While doing this have the mouse switch on/up/green and assure that each 3.7v cell inserted individually make contact (e.g. mouse's green LED above switch comes on after a couple seconds). You want to use both cells in parallel to get good battery life.

The mouse I performed this surgery on has been working perfectly for days now and still reads 100% (due to 3.7v+ vs expected 3v+). I expect good life out of these batteries because of their higher nominal voltage & good mAh.

Again, because the mouse's low battery warning & cutout are below the protected cell's cutout (~ 2.7v) you may not get a low battery warning prior to the mouse losing connection. I mitigate this by using the widget "BatteryLevel" & occasionally hitting F12 to see battery status. There will be a target % of battery life that represents about 2.9v and this is the time I'd choose to swap in charged 14500s. But I'll probably just use the mouse until it dies then swap the cells.