In all the years I’ve been road testing cars, I have come to admit that proximity keys are kind of nice. There’s something easy about never having to fish around in your pocket for a key that’s somehow buried itself beneath your wallet and garage door opener, and when you spend time with multiple different key fobs, proximity entry means no hitting the wrong button in the dark. However, beyond potential security issues with some setups, most proximity key fob applications do come with one big downside.
Replacing a key fob battery is a bit of a pain. Not only do dead button batteries mean you have to mess about with a tiny key blade, cracking open a key fob feels like surgery. One wrong move, and suddenly you’ve broken the aged, brittle clips that hold the two halves of the key fob shell together. Also, certain styles of key fob use battery holders that are easily sheared off the board if you have appendages made of ham. Plus, a good button battery is a couple of bucks these days, and that’s just an unexpected nickel-and-dime expense every couple of years.
You’d think by now that we’d have solved the issue of key fob batteries running low. It turns out, BMW did ages ago, but the advent of proximity keys basically killed that feature off. However, hope might not be lost. The digital, connected era means you might already have a rechargeable key fob for your car without even knowing it.
Starting in the 1990s, BMW rolled out a diamond-shaped key with a serious party trick: inductive charging. Yep, the same technology you use to recharge your smart watch. Simply slot the key into the ignition, turn the car on, and inductive charging would juice up the key fob battery on a long enough run, meaning that theoretically, you’d never have to replace a key battery again, so long as you followed the instructions, rotated out both key fobs, and went on periodic longer drives.
When the 2000s rolled around and RFID immobilizer-based contact push-to-start technology rendered physical key blades unnecessary, BMW kept the inductive charging on its base line of fobs. Basically, you’d slide the plastic key fob into a slot in the dashboard, then push a start button to fire up the car. Once in the slot, inductive charging would give the key fob a helping hand so it can theoretically stay charged up.
By the mid-2000s, however, proximity keys were making their way into the mainstream, featuring rolling radio codes and touch pads on door handles that meant you’d never have to remove the fob from your pocket. Obviously, people weren’t sliding these keys into the dashboard, so BMW went with a replaceable button battery once again. That’s a couple bucks every few years, and some hassle to install a new cell.
Of course, going back to button batteries solved an often user-induced issue with rechargeable keys. BMW’s inductive charging keys were sealed, meaning that if the batteries were allowed to run flat, the only way to fix it involved slicing open the fob and desoldering the battery inside to replace it. While some early fobs used according to BMW’s instructions are still functioning nearly 30 years later, some aren’t.
Still, even when proximity keys started to dominate, BMW didn’t give up on rechargeable keys entirely. Remember that hilariously hefty Display Key from the 2010s with its own built-in touchscreen? Yep, in addition to USB charging, it could also charge inductively when set in the car’s wireless phone charger. Probably best that it stayed out of your pocket while driving, considering this monster fob’s about the size of a hamster. That could get uncomfortable on long road trips.
Flash forward to the present day, and the latest sensation is phone-as-key technology, now offered by a huge range of manufacturers from Tesla to Hyundai. Using either Bluetooth Low Energy or Near Field Communication, owners of some modern cars can lock, unlock, and start their vehicles using their phones. Think of it a bit like Apple Wallet or Google Wallet, but for your car. Plus, since your smartphone doesn’t run on button batteries, it means you might already have a rechargeable key fob for your modern car. In some ways, what’s old is new again, although it is quite neat that BMW pretty much solved this common aggravation nearly 30 years ago.
Top graphic images: Thomas Hundal; BMW
Everyone had their own preferences, but Until/unless they can make a phone that’s lasts weeks on a charge, replacing a cr2032 every few years is preferable for me. No way do I want to get stranded at the trailhead after a camping trip because my phone died and now I can’t start my car.
Even if the fob battery goes entirely dead, in my car I can open the door with the metal bit and press the fob into the start button and it will start (it uses RFID or something similar that doesnt require the battery as a backup to the normal proximity).
My wife has an i4, which has been great. The only real reminder we’ve had that the car is a BMW was when I replaced the battery in the key fob.
After a year or so, we were getting warnings on the dashboard that the key fob battery was empty. No problem, grabbed a pack of Duracells from the store (not Amazon counterfeits) to replace it. Continued to get the warning on the dashboard after the battery was replaced. It still worked fine (actually at no point did it ever stop working), so asked the dealer next time we were in.
Turns out the key fobs are very picky about what brand of (standard) coin cell battery you use. The dealer swapped our battery for an original BMW Varta (for free), and the message went away. Interestingly, they proactively replaced both key fob batteries for free during our last service.
Thats not exactly a “bmw” thing. While there is a “standard” for batteries of this size there are slight variances in both manufacturing size tolerances and voltages/amps. Some give you a little extra juice some stick to the official specs. I did home security and the window sensors hated energizer cr2032s and if you did not use lithium AAs on the key pad it wouldnt work. It was very annoying thing for both me and the customer having to deal with those “i replaced all the batteries and now the alarm doesnt work” calls it wasnt user error just the equipment wants what it wants. But hey it kept food on the table!
My best mate just had the battery in the key fob for his latest car run out, and it was then that he found out that the spare key was also dead.
When he replaced the batteries he found out that the spare key wasn’t just dead, it was empty. No circuit board, nothing.
I’ve always like the BMW inductive diamond keys. 24 years on the ones in my parents e38 still work great, though you do need to use them occasionally to make sure they don’t loose their charge.
Urgh. Volvo/Polestar have two kinds of keys. One is a big chunky conventional “comfort access” key, with a button battery in the back that’s changed easily enough.
The other is a little fob thing. There are no buttons, it’s proximity only. And it’s waterproof, so you can go do “lifestyle” things and not kill it! Yay!
That also means it’s sealed. And not rechargable. And so it dies after a few years and you either hack it apart and put the circuit board, with a new button battery, in a 3D printed enclosure, or pay your local dealership a fortune for a new one. They’re also often missing from used cars. Because they stop working and get chucked away. But to activate the car’s app, you need *all* the keys in the vehicle for it to work.
I love my Polestar, but this is such a stupid setup.
“That’s a couple bucks every few years, and some hassle to install a new cell.”
Ha! I wish it were that easy. My mom’s new Mercedes chews through fob batteries roughly every 3 months.
Is she keeping it near the car when at home? A lot of key fobs keep a radio link between the key and car alive, and if you keep the key in the car or close to it battery will die quickly like you describe. Get it out of range and the battery lasts much longer.
The car is parked pretty far from the house, so it should be out of range.
On the “brick” key in your hero image, which was in use on the later E-chassis cars (E60, E61, E63, E64, E70, E71, E89, E90, E91, E92, E93, etc)…there were two variants. Cars with “Comfort Access,” which was BMW’s term for fully keyless operation, had removable batteries, because you wouldn’t stick them in the slot under normal use. Cars that didn’t have Comfort Access had the removable battery, because you’d always stick them in the slot to operate the car.
Ditto with MINI during the same era.
“...Cars that didn’t have Comfort Access had the removable battery…”
I’d vote for a missing “…didn’t have…” in the above statement