Advanced Battery Applications Blog

Complex battery usage consultancy from Dave Morris
Home / battery life / Are you killing your laptop battery by overfeeding it?

Are you killing your laptop battery by overfeeding it?

A question often asked is ‘Why does my laptop battery not last as long as it used to?’ A simple question you may think, but is it a question about run time between recharges, the number of times the battery can be recharged, or both?

The clamour to plug into the few available power points at the start of a meeting, with moans about how the battery in this laptop is rubbish (or similar) comments is a situation many will identify with. Many of us regard a laptop computer (or increasingly notebook) as a vital piece of equipment enabling us to do our jobs ‘on the move’. But just how often is the laptop really being used on battery power? Most will have a docking station at the workplace and/or home office, so without fiddling with plugs and cables we are instantly connected to everything we need – including to mains power. Be honest now, how many times and for how long do you really need your laptop to be powered by its internal batteries?

Overcharging when your laptop is docked

For batteries used in this type of application, one of the main ageing factors is the amount of overcharge the battery is subjected to and the temperature at which it occurs. In the early days of laptop computers, typically the battery type fitted would be Nickel Metal Hydride (NiMH). This early generation of laptop batteries gave the leap in energy density required to make a portable computer practical, but a drawback was a fairly hefty self-discharge rate. This meant that it was a necessary practice to keep the battery ‘topped up’ on charge. Although this was adding to the ageing of the battery, this was to some extent masked by the bigger capacity fall off if the battery was left off charge.

The advent of Lithium Ion batteries gave another big leap forward in the amount of energy that could be stored in a given volume and weight. The trouble is that headline figures for run time for your new laptop are based on having every last drop of capacity squeezed into (and then out of) the battery. It is not long before the laptop struggles to meet this performance figure.

One of the drawbacks with lithium ion batteries is that keeping them at high states of charge results in a permanent loss in the energy the battery can store.

If the battery is kept at 100% state of charge for any length of time, for example when the laptop is plugged into mains power, you will get a nasty surprise when you try and run it from its internal power source. Especially when the low battery flag appears after a short period of use mid-way through a crucial action (admit it, it has happened to you!). Refer to a previous blog where I asked ‘What is the battery indicator on your phone really telling you?’ to understand why!

But is there anything you can do about it?

By keeping to old habits, and keeping the battery ‘100%’ charged you are actually reducing amount of energy a fully charged battery can hold. Lithium ion batteries have a much lower self-discharge rate than the NiMH batteries they replaced, so there is no need to keep the battery ‘topped up’. By doing so you are killing the battery by overfeeding!

The good news is that there are things you can do to reduce this ageing effect, especially if you are one of those people who rarely use their laptop on battery power. Perhaps the most drastic is removing the battery from the computer when plugged to the mains, but we can do better than that!

Change your laptop settings to limit charging from mains

I was pleasantly surprised when setting up a new laptop recently to find that it had a built in charge limiter that, if left on mains power, would not charge the battery to more than 75% state of charge. Ideal where the anticipated usage meant it would be run frequently from mains power. It was something that had to be activated, and the feature was buried in the settings menu, but something I would advise searching for, especially if you have a new laptop.

Manually disconnecting the laptop battery

Not as convenient as it requires user intervention, an alternative method is to use the state of charge indicator and disconnect from mains power if the battery is showing a state of charge of more than 80%. But it is important to remember to reconnect when it falls below 30%. There will still be the usual ageing associated with cycle life going on, but this is not as severe as leaving it on permanent charge.

Although at first the autonomous run time of your laptop will be less than that for a ‘100%’ charged, ‘overfed’, new battery, it will not be long before the cross over point is reached, maybe only a few months, and your managed battery will give better run times on those few occasions where there is no mains power.

Recent Posts

Start typing and press Enter to search

choosing your battery solutionElectric Powered Vehicle Electric powered Aircraft Electric Transportation