Like most people, you probably plug your smartphone into the charger when you go to bed and leave it plugged in until you wake up in the morning. Nobody wants to start their day with less than a full charge, and you have plenty of time to get that charge overnight while you’re sleeping anyway. The problem is that following that strategy can actually be bad for your smartphone’s battery and can eventually reduce your battery life. To combat that without sacrificing the convenience of overnight charging, Bornach developed a device for “Calorie Restricted Phone Charging.”
Older battery types that are now largely obsolete, such as NiCd, required specific charging strategies in order to maintain battery life. For example, you want to let a NiCd battery fully discharge before you fully charge it again. The good news is that LiPo batteries — the kind found in virtually every modern smartphone — don’t require quite as much attention. Unfortunately, that overnight charging can be a problem. Your phone should reach a full charge within an hour or two. The rest of the night it will bounce back and forth between 99% and 100% as it consumes a small amount of power and then recharges. That can reduce your smartphone’s battery capacity after a year or two.
Bornach’s solution was to build a device that sits between the smartphone and its charger in order to charge up the battery in an optimal manner. This device has a Microchip ATtiny85 microcontroller that measures the current passing through the charging cable via a MAX471 current sensor. That gives the device the ability to monitor how much current is going into the smartphone and how long it has been charging. A simple MOSFET chip can then be used to switch off power to the smartphone once it has reached the proper battery charge — and then leave it off for the rest of the night. If you’re concerned about maintaining your smartphone battery, you might want to consider making a device like this.