Lithium ion battery fuel gauging is now accurate enough for medical apps

After writing about the end of the mostly useless fuel-gauge last week, I read some of the post’s comments from readers that were a little cynical about the likelihood of the fuel gauge being significantly more accurate than previous generations of gauges. Certainly vendors have always claimed that their parts provided amazing levels of accuracy. So just how real is TI’s Impedance Track algorithm and chip at measuring the amount of juice left in a rechargeable lithium ion battery pack?

I called up Dr. Robin Tichy, the battery guru at battery-pack design house Micro Power. I was half-way expecting an equivocating answer about how she hadn’t tried it yet, too soon to tell, blahblahblah. But she immediately said words to the effect of hoo-boy, that stuff really works. Her poster-child example was medical electronics used for life support applications: One of the requirements for life support apps containing batteries is that you have a precise countdown from 30 minutes left of battery life. As a result, most life support electronics relied on a sealed lead acid backup battery rather than lithium ion because lead acid batteries have a predictable discharge profile: Their predictably constant slope makes them easy to fuel gauge. Lithium ion’s discharge profile is pretty constant until just before it’s completely discharged, when it knees almost straight down. However, Tichy says MicroPower can now use lithium ion backup battery packs in critical medical applications because the Impedance Track gives an accurate gauge on the remaining battery power. She definitely sounded unequivocally happy with the technology.