Battery Brains: Beware The Drains

My long-time colleague and mentor, Bill Schweber, is unfortunately now cranking out content for a competitor. His formidable writing skills have survived the employment transition intact, judging from his columns that have recently begun regularly appearing in print. Take a look at, for example, ‘When an on/off switch really does that‘, which I particularly enjoyed.

Schweber’s insights helped explain an initially baffling issue that confronted me last week. I regularly used to carry two spare Li-ion batteries along with my Dell Inspiron 700m, in case I was confronted with a long work day (or a long commute) without AC access. Even if I didn’t use a particular spare for six months or more after charging it up, I’d inevitably find it still nearly full-charged the next time I plugged it into the laptop. Imagine my surprise, then, to encounter a completely sapped spare lithium polymer MacBook battery last week…one that rebuffed my subsequent attempts to revive it.

What happened? When I bought the MacBook last November, I also purchased a spare battery for it. After initially charging the spare up, I put it aside, since I wasn’t yet using the MacBook full-time, and assuming from past experience that all would be well. Obviously, I was wrong. And this Apple support document gave me a clue as to the probable reason why things were different this time around.

If your MacBook or MacBook Pro’s battery is fully drained of power, the battery will put itself into a low power state to preserve its ability to charge in future…please allow the battery up to five minutes to come out of its low power mode and begin accepting a charge again…

This all means that the MacBook battery, unlike its Inspiron 700m predecessors, contains built-in ‘intelligence’. In retrospect, I should have already known this, since the MacBook battery includes a button that, when depressed, provides a LED readout of its charge state even when it’s not mated to the computer. Built-in intelligence (whether analog, digital or a mix of both) requires a power source in order to keep working. That power source is the very same battery it’s simultaneously monitoring. And apparently, the built-in intelligence can drain that very same battery in about nine months’ time.

Fortunately, the MacBook’s still under warranty, so Apple shipped me out a replacement battery last week. Going forward, I’ll need to remember to proactively swap out batteries every month or so. Sigh. I’m reminded of a print column I wrote and EDN published back in July 2002, which surprised (judging from the feedback I got) and alerted many readers to the fact that modern batteries (like their lead-acid, alkaline and NiCd predecessors) are also prone to ‘memory’ issues.

In thinking back over the MacBook situation last weekend in preparation for writing this column, I realized that Schweber’s wisdom explained another battery-related issue I’d recently begun seeing, this with my Sandisk Sansa Connect portable multimedia player. I’m no longer running with headphones jammed in my ears, so the Sansa Connect gets less use than it previously did. Nowadays I might go a week or more between power-ons, and when I do I inevitably find that the battery’s near-to-completely drained in spite of the fact that I’d fully charged it prior to putting it away.

If you quick-depress the on/off switch, the Sansa Connect goes into a standby mode that delivers fast subsequent wakeup but also, apparently, incurs substantial continued power draw. To more fully shut down the device, you need to continue holding down the on/off switch for several seconds. You end up with a roughly 1 minute long boot-up delay the next time you use the device, but I suspect you also end up with much longer shelf life between charges. Maximizing usable device life between charge cycles is particularly critical when the device has a non-replaceable battery and therefore becomes a paperweight once that battery no longer holds a meaningful amount of charge.

Another of Schweber’s recent columns, ‘Too much information, or too little?‘, also has a personal resonance. A few months back, we incurred a four-digit repair bill at the local Volkswagen dealer after growing tired of worrying about a ‘check engine’ light on our Eurovan Camper, which regularly appeared (and disappeared) even though it didn’t correlate to rough idle, uneven acceleration or any other perceptible problem. As it turns out, the engine was (as we suspected all along) fine…the sensor board had failed. And now my wife’s Toyota Matrix has an illuminated ‘check engine’ light, too. Sigh, again…

p.s….I thought I was done writing about my MacBook for a while, but I guess not! Apparently it, like its predecessor, will be an ongoing muse.