Laptop always plugged to charger: how to properly keep the battery's lifespan

Question

I provided my HP Probook laptop with a 9 cell 6900 mAh battery, which obviously gave good autonomy. I always keep it plugged in to the charger.

I noticed (and I guess that is due an embedded function in the BIOS or in the battery’s circuit) that as soon the battery percentage reach 97%, the charging process restarts: I mean that as 100% is reached, the charging process stops, and until 98% is obviously reported “plugged in, not charging” and when 97% is reached, the charging process starts again. I utilize such laptop for several hours during the day (I would say for about 8 – 9 hours) and I see such process (charging from 97% to 100%) for about two or three times. I have to say that this charging process from 97% to 100% takes almost/less than 10 minutes: is very quick, so – at least in terms of temperature – the battery shouldn’t suffer too much.

What makes me puzzled is to see these brief charging sessions every day, and by searching on some guides and how-to about properly keep laptops batteries, seems that to maintain a wise lifespan of the battery, the charging sessions should be reduced, but is not my case, and I fear that on the long term, the battery will last less than normal.

Furthermore, on the HP Notebook PCs - Improving Battery Performance's page, they claims:

To protect the battery from multiple, brief charging sessions when you connect the power cord, the battery does not begin charging until the charge falls below 94%.

But in my case, this happen on 97%.

So, here main questions: maybe would be a good practice to unplug the charger after that battery reached 100% of the charge and plug it again, eg, on a lower percentage, like 40%? Or maybe even better (as someone else claims) keep in the 40 - 80% range? I cannot figure out, in terms of strain and battery's lifespan, if is better to do these brief and quick charging sessions for 2 – 3 times at day (from 97 to 100% in about 10 minutes) or lessen them at the cost of more time spent in the charging process (should take about 1 hour to go from 40% to 100%), and so increments the charge/discharge cycles, which could also increase the battery’s temperature (more time spent in the charging process).

Answer 1

This is a pretty broad question, as different batteries do different things. There are some basics we need to understand about battery charging in order to answer.

1. Battery indicators are unreliable. Ever had an iPhone that dropped from 50% to 11% in a matter of seconds? That's because the actual battery measurement hardware is usually cheap junk. The difference between an indication of 94% and 97% can be pretty arbitrary, especially if the indicator is measuring the amount of electricity leaving the battery and not the amount of electricity stored inside (which is usually how it works).

2. Battery charge shutoff is a thing. There was a time where you could "overcharge" a battery by leaving it plugged in, but most decent electronics now disconnect the battery from the incoming power when the battery reaches 100% charge. Remember, battery measurement hardware is usually cheap junk. If you've got a good, high-end laptop, chances are you can trust its regulator to cut off the battery appropriately. If you have a Wal-Mart Acer or Gateway that was not only on sale, but came with a free copy of a Deer Hunter game, don't trust that regulator. Phones are the same way; that's why even though a Samsung Note Awesome Edition will tell you to disconnect its cord at full charge just as much as an offbrand FailurePro 2000.

3. Memory isn't a thing. You may hear that you should always charge to 100%, because if you don't, you set the battery to only charge up to a certain point. This is known as "memory", as well. It's also not a problem anymore. This is because Lithium-Ion batteries do not work on the exact principles as Nickel-Cadmium batteries did, which do have the memory effect. Ni-Cad are also the batteries that usually overcharge to the point the casing starts getting wobbly like a waterbed and will catch fire during use if you try when it's like that.

With all of that understood, the answer becomes "it depends on the battery and the hardware". The real reason to avoid multiple burst charges is because this tends to pass a small power surge through the battery, repeatedly. That is taxing on the hardware for the actual power socket, as well as the battery bay, and is undesirable. This can, in turn, damage the battery. What the manufacturer is referring to, however, is preventing the rapid power ebb and flow of dropping to 99% and then charging back up during use, over and over. That could happen hundreds of times per second, which is much different than you just plugging it in when it hits 95%.

As far as the overall life of the battery, chances are that it will last as long as you will use the device. Modern batteries don't have the worrying limits to charge repetition that they used to have, but if it's an honest worry, it's less trouble just to keep an extra battery on hand in case your existing one refuses a charge one day.