It took me a long time to really pay them any attention, but Motorola has offered Impres-branded batteries for their handheld radios for a long time, and they're actually pretty nifty.
The idea is that there's a chip on the batteries giving them some "smarts." Particularly in the days of Ni-Cd batteries, their "reconditioning" step could help minimize the impact of the memory effect, with the charger periodically running the battery down all the way and then refilling it.
It turns out there's a lot more going on behind the scenes. During the reconditioning step, the charger also keeps track of how much of a charge the battery takes and calculates what percentage of its rated capacity remains. Some of the fancier gang chargers have LCDs and will display this information, but even the simpler chargers will start giving you a flashing red-and-green light to let you know the battery is wearing out. It seems like the "killer app" here is public safety applications–it's a minor annoyance for me if a radio I'm effectively using as a scanner starts to only last a few hours before I have to swap batteries. But for something like law enforcement, being able to know whether your battery will last your full shift seems like a much bigger deal.
I recently picked up an Impres "Battery Data Reader," which looks a lot like a standard charger, but it has a USB port on the back and doesn't charge. It reports data like this:
This is the case of a totally dead battery, and which seems to have suffered some data corruption. (Not a great example, Matt!) The red/pink fields couldn't be read due to corruption, but we can see that the battery was rated for 2100 mAh, but now only supports a "potential capacity" of 474 mAh.
It also reveals that Motorola's "rated capacity" is actually conservatively rated; it's apparently the minimum spec for warranty purposes. This one apparently took 2781 mAh when it first went into use (April 10th, 2014).
Reading a bit about this and the extended user guide, the battery also has a real-time clock and some memory. It appears that the clock is set at the factory and only needs to be accurate to within months, so periodic syncing isn't supported (AFAICT), except for the special case when the battery has been "overdischarged" and, I infer, the RTC stops ticking. The reader is seemingly the only way to reset it.
The memory supports more than just a simple count of charge cycles; it differentiates Impres from non-Impres cycles, and even keeps a histogram of the battery's charge level when first inserted into the charger:
You can see that this one tended to be put back in the charger when it was still 50-60% full. I'm not sure what you're supposed to do with that data; the whole idea of Impres batteries is that you shouldn't need to run the batteries out before charging them. This particularly battery looks like (based on its labels) like it came out of a prison facility; perhaps what the graph shows is that the battery was typically listing more than a shift, with the user presumably dropping it in a charger at the end of the day with 50-60% charge still left?
I've learned from reading a bit that the "potential capacity" (474 mAh in this case) is computed when the radio goes through a reconditioning cycle, and is used by the "fuel gauge" on radios to show how full the battery is. This also matches my experience with some old batteries that came from a lot of radios I bought at a hamfest–capacity indications were all over the place until a few conditioning cycles.
Also interesting–at least to me–the application keeps a running CSV file of everything it reads. It'd be interesting to write a little app that would take that file and track this data over time.
As an aside, the gang chargers have what's apparently an HD15 port on the back (which looks suspiciously like, but is not, a VGA port). There's not a whole lot of information out there except for this Batboard thread about it. There's apparently this adapter for it that will hook up to a PC, which can integrate with their "Fleet Management Software." The Impres reader app also supports sending data there. It appears that there's a trial at https://www.motorolasolutions.com/en_us/products/two-way-radio-accessories/batteries/impres.html, but what I'm really interested in is what's reported off the back of the charger. You could rig up something with a Raspberry Pi to grab the data without all this stuff?
In conclusion, I lead a pretty exciting life.