If you want to maximize the life of your lithium-ion batteries, proper storage voltage is critical. That is, don’t store them empty, and don’t store them completely full either. “Almost fully charged” is a sweet spot for occasional-use devices. Sadly, this is easier said than done. While many devices use integrated rechargeable batteries these days, most provide no method of limiting charge level. That’s where [DaverDavid]’s ChargeCap comes in.
ChargeCap sits between a USB charger and target device, disconnecting when it detects that recharging is 80 to 90 percent complete. This is particularly useful for maximizing the cell life of devices that see only intermittent use.
The way ChargeCap does this is clever, and relies on the fact that all lithium-ion charging curves look the same regardless of cell capacity or cell count. Charge current remains at pretty much the same level for most of the charging process, but tapers off quickly (and in a linear fashion) as cells approach their maximum capacity. That’s because charging a battery is a lot like blowing up a balloon: the first breaths are easy, but once the balloon fills out, every breath needs to push harder than the last.
ChargeCap works by sampling the peak charge current at the beginning of the charge cycle, then detecting when it drops below 50 percent of peak, at which point charging is stopped. The result is a device that reliably charges to 80 to 90 percent of capacity, and no more. ChargeCap uses an ESP32-C3 and a small OLED display that, as a nice touch, inverts colors to signal charge completion. Design files and code are at the GitHub repository.
Lithium-ion cells are fantastic devices, so flesh out your knowledge by reading [Arya Voronova]’s primer on designing them into your own projects, or a more in-depth explanation of how they work.
My phone has USB-C fast charging but I (almost) always charge it using a 500mW USB-A charger, charging it almost every night. It is almost 5 years old (so having had close to 1800 charges) and I notice hardly any degradation on the battery, I can still walk a full day (±9 hours) with GPS recording on on one charge, provided I disable Wifi and one of the two sim cards.
Yup, newer Samsungs (possibly all Androids?) have a settings toggle for “Fast charging” – i think it flips between 10W and 25W. I have fast charging disabled (use it about once a month when i need it) and after 22 months my phone reports 100% battery lifespan and 623 charge cycles.
If you charge your phone overnight, iPhones charge to ~80% and then hold until just before you get up.
MacBooks only charge to ~80% if you leave them plugged in. If you want to totally fill them up, there’s an option on the battery menu.
this is a neat idea. i really wish there was a way to do something like this on retired cellphones by configuring the built-in battery monitor. when it’s in daily use i enjoy charging it all the way (i suppose), but when i retire them, they sometimes wind up sitting on the charger 24/7 and instead of providing a brilliant battery backup for power outages, eventually it winds up cooking the battery one way or the other.
“That’s because charging a battery is a lot like blowing up a balloon: the first breaths are easy, but once the balloon fills out, every breath needs to push harder than the last.” What??? Blowing up a balloon is exactly the opposite of that.
Blowing up a balloon is hard, then easy, then hard.
Like a battery. The (Electric bus) batteries I work with have very slow charge speeds (sometimes 15kW, while between 10-80% they can usually charge at 150 or sometimes up to 450kW) for the bottom 5% technical SoC, which is why we (and many manufacturers) set them to never go below 10% technical SoC.
For anything involving a single battery cell (“3.7v”, “4.2v”, etc) this is a brilliantly simple solution. For something with multiple cells, like the 7.2v workpro glue gun(?) in the photo, it’s still probably good, but the benefit is a little less clear-cut.
To maximize the lifespan of multi-cell lithium batteries, proper cell balancing is also important, and devices that use “top balancing” are pretty common. It’s a simple, cost-effective method that uses resistors to bleed off charge to some cells and allow the undercharged ones to catch up. Unfortunately, that means it doesn’t usually kick in until the battery is closer to fully charged than this device will allow.
So, that means you should probably still charge such devices to 100% every once in a while to maximize their lifespan, but unless you have some way to measure the voltage of each cell separately, there’s no good way to know when “once in a while” actually is.
(and if you have a way to measure cell voltage independently, you also probably have a way to implement your own balancing solution that solves this problem)
If this really works on any device, this is an awesome invention. I’m slightly surprised that lots of devices don’t do weird things though… I guess this relies on the vast majority of the current being charging, and the device not having any clever charge strategies?
You would think that this kind of intelligent lithium battery management would already be built into rechargeable devices by now, wouldn’t you?
(or at least hope that…)
My poor man’s solution has been to run my phone’s charger on an hour and a half time limit, which will generally stop it before (the phone reports) 100% charge.
Of course I also use a lower powered phone with a larger battery, so I don’t have to charge it all the way up for it to be useful all day.