More life from your batteries

If you're like me you long ago gave up on trying to remember what to do with all the rechargeable batteries in our lives. Fully charge? Let them go dead before charging? What?

Popular Mechanics went after this question and basically acknowledged the confusion. Here, the magazine says, is what we do know.

The safest life for lithium-ion is one of moderation. The only way to minimize all of the factors that eat away at capacity is to pretend that there's less effective capacity. Never charge the batteries to 100 percent, and never let them come close to empty. The narrower that band of charge and discharge, the better, since what amounts to the cells' metabolic activity slows at 40 to 60 percent capacity. Chevy takes the choice out the user's hands, keeping the Volt's battery within a range of 20 to 80 percent charge.

Isidor Buchmann, founder and CEO of British Columbia-based battery-testing firm Cadex Electronics, has no proof, but suspects that the higher cycle counts of Apple's newer built-in laptop batteries use a similar approach, cutting off the voltage to cells before they reach 4.2 V. Whether it's true or not, that appears to be the best strategy for the current generation of li-ion (particularly the cobalt oxide variety found in consumer electronics). Ignore cycle count, and focus on keeping gadgets as close to half-full as circumstances permit. Full batteries are fine for travel, dead batteries are an unavoidable setback, but for day-to-day operation, let the Goldilocks standard be your guide.

Here's one other thing we know: Leaving li-ion plugged in is a problem. Even when persistent heat is not an issue, a constant state of charge is tantamount to working your batteries to death.

I'm not sure we've figured this thing out yet.