[Surferdude] was unhappy with the decreasing life of his aging uninterruptible power supply. He decided to beef it up using marine batteries. He extended the battery connections outside of the UPS case using #10 wire and swapped the two 12 volt gel cells with the heavy duty lead-acid batteries. Doing so upgraded the device from 20 amp-hours to 84 amp-hours at a cost of about $160. If you’re thinking about taking this on yourself, pay attention to the countinuous output rating of your UPS to prevent a fire risk.
Looks like they’re at it again over at Adafruit. This time they’ve produced a clock that looks more like it should be attached to a munition rather than cruising bedside. But, geek-cred aside, there’s a lot to be learned from their design. Like we’ve grown to expect, they’ve put together some good documentation on their choice of components.
Start off by taking a peek at their 5v power regulator. There is an extra diode on the output side that prevents reverse current from the 3v backup battery. The AVR ATmega168 that controls the clock is used to detect loss of power and quickly shift to the battery backup. They’ve also used the microcontroller as a boost converter for the high voltage VFD, a nice trick we’ve seen before.