How much exactly will using my laptop on AC destroy my battery?
“It really all comes down to which laptop you have. IBM/Lenovo, Gateway, and Dell tend to use — in most models — fairly shitty charge circuitry (and/or badly-chosen charging parameters) that eat away at the battery somewhat more aggressively when left to cook on AC.” I was under the impression (from examining the charging circuits on a sample of laptop motherboards) that the designer pretty much slaps on one of the all-in-one charging ICs, like the DS2715 and they’re done with it — not much engineering goes on on the part of the laptop manufacturer.
Dont worry about it. I had the same concern a while back, but as far as I can tell, it was groundless – I’ve kept an eye on when the battery is being topped up, and if yours is anything like mine (which it probably is) and you run it off AC most of the time (as I do), the top-up’s are infrequent enough that the oxidation shelf-life of the battery will kill it long before you run out of charge cycles, so to speak. (Mine seems to let the battery get below 95%, probably lower, before topping off, and since the only major drain is when I unplug the running laptop to move to an AC outlet in a different room, it won’t top off more than once a day, usually a few days between top-offs. If you DON’T run it off AC, and thus deplete it and recharge one or more times a day, every day, you’ll probably hit the charge cycle limit before the shelf-life limit. The shelf-life limit can be pushed back a little bit by keeping the battery cool. If you wanted to be anal about it, you could store the battery
My nickle’s worth… I have spent the last few weeks reviewing battery chargers for several battery species (sealed lead acid, NiCad, NiMH, LiPo, etc) Also, I’ve designed a number of chargers over the years. IAAEE, btw. Your laptop, almost without doubt, has a sophisticated charger that maintains it fairly well… The question you seemingly asked is does leaving it plugged into AC make a difference in long term life? How should you change your use to optimize battery life? That’s kind of a hard question, but remember, the designers had something in mind when they chose what they chose. Probably, it was portable operation off grid, which is not what you are doing. Your use pattern sounds like desktop, not laptop. (It prompts the question of why you care, almost. Mostly, you’ve got an integral UPS!) Anecdotally, I use my 4 year old Thinkpad A31p 99% of the time plugged into AC, and that’s 8 hours/day, 5 days a week on and plugged in the rest of the time. I have dual batteries. THey have
TomsHardware (err… MobilityGuru) just did a huge report on this here. Given that their “Lessons Learned” seem rather opposite to the replies here, you’ll have to make a decision on which you trust more. Personally, I have had great luck with my laptop batteries, but I don’t leave my batteries in my laptop after they are charged. I recently retired my 4-year-old Dell Inspiron with dual batteries… I was getting about 50% battery life out of them at the time, which I feel is pretty awesome. When my brother’s school forced him to buy a laptop (part of the nursing program), he asked me what he should do, I suggested removing the batteries if they are charged. At the end of his first year, he was the only one in class that could make it through the class without plugging into the wall… The school A) tells all students to remove batteries as soon as they are charged, B) no longer deals
For reference, I’ve done some tests (unplug the cable for a minute, plug back), and I’ve found out that: 1) If the cable’s plugged and the battery is above the threshold, the charge reported in the windows power meter is 100%. 2) The threshold is 93-94%. After that, the laptop starts charging the battery, and the windows power meter shows the true charge level. What I’m yet to test is the loss rate for the battery while the laptop is on AC. What I can say is that it is certainly less than 2% per day for my usage profile. So, in the worst case, the battery will be topped off once every 3 days, which seems good enough for me. I wish this threshold were user-configurable, though. I gather that having it at 90% (or even 85) would fit my needs better, with no relevant impact on off-grid use.
