Calculator Battery Mod Lets You Go The Distance

September 23, 2025 by Dan Maloney 23 Comments

Disposable batteries seem so 1990s. Sure, it’s nice to be able to spend a couple of bucks at the drugstore and get a flashlight or TV remote back in the game, but when the device is a daily driver, rechargeable batteries sure seem to make more financial sense. Unfortunately, what makes sense to the end user doesn’t always make sense to manufacturers, so rolling your own rechargeable calculator battery pack might be your best option.

This slick hack comes to us from [Magmabow], who uses a Casio FXCG50 calculator, a known battery hog. With regular use, it goes through a set of four alkaline AA batteries every couple of months, which adds up quickly. In search of a visually clean build, [Magmabow] based the build around the biggest LiPo pillow-pack he could find that would fit inside the empty battery compartment, and planned to tap into the calculator’s existing USB port for charging. A custom PCB provides charging control and boosts the nominal 3.7-volt output of the battery to the 5-ish volts the calculator wants to see. The PCB design is quite clever; it spans across the battery compartment, with its output feeding directly into the spring contacts normally used for the AAs. A 3D-printed insert keeps the LiPo and the PCB in place inside the battery compartment.

Almost no modifications to the calculator are needed, other than a couple of bodge wires to connect the battery pack to the calculator’s USB port. The downside is that the calculator’s battery status indicator won’t work anymore since the controller will just shut the 5-volt output down when the LiPo is discharged. It seems like there might be a simple fix for that, but implementing it on such a small PCB could be quite a challenge, in which case a calculator with a little more room to work with might be nice. Continue reading “Calculator Battery Mod Lets You Go The Distance” →

LED Driver Circuit For Safety Hat Sucks Single AAA Cell Dry

January 19, 2023 by Donald Papp 21 Comments

[Petteri Aimonen] created an omnidirectional LED safety light to cling to his child’s winter hat in an effort to increase visibility during the dark winter months, but the design is also great example of how to use the Microchip MCP1640 — a regulated DC-DC step-up power supply that can run the LEDs off a single AAA cell. The chip also provides a few neat tricks, like single-button on/off functionality that fully disconnects the load, consuming only 1 µA in standby.

[Petteri]’s design delivers 3 mA to each of eight surface-mount LEDs (which he says is actually a bit too bright) for a total of about 20 hours from one alkaline AAA cell. The single-layer PCB is encased in a clear acrylic and polycarbonate enclosure to resist moisture. A transistor and a few passives allow a SPST switch to act as an on/off switch: a short press turns the unit on, and a long press of about a second turns it back off.

One side effect is that the “off” functionality will no longer work once the AAA cell drained too badly, but [Petteri] optimistically points out that this could be considered a feature: when the unit can no longer be turned off, it’s time to replace the battery!

The usual way to suck a battery dry is to use a Joule Thief, and while this design also lights LEDs, it offers more features and could be adapted for other uses easily. Interested? [Petteri] offers the schematic, KiCAD file for the PCB, and SVG drawing of the enclosure for download near the bottom of the project page.

Squeezing The Juice Out Of Some AA Batteries

February 27, 2012 by Mike Szczys 75 Comments

[Ray’s] breadboard power supply lets you drain the last traces of power from ‘dead’ AA batteries. Electronics that are powered off of disposable alkaline batteries have a cutoff voltage that usually leaves a fair amount of potential within. Since many municipal recycling programs don’t take the disposables (you’re just supposed to throw them in the trash!) we love the idea of squeezing them for prototyping use.

His design uses just one IC, the MCP1640, along with a handful of passive components. The chip is a boost converter with a startup voltage of just 0.65V, which means the batteries themselves – normally starting life above 1.5V – can be used until they drop to about 0.3V each.

Above you can see the kit he is selling. But it’s an open source project and the circuit is so simple we’re sure you can build your own. Add that boost converter chip to your next parts order for around $0.40.

[Ray] made a nice demo video for the device which you can see embedded after the break.

Continue reading “Squeezing The Juice Out Of Some AA Batteries” →