Batteries

Replacing a laptop battery: how to find the right one

A laptop battery that drains quickly, only works on the charger or has swollen up needs replacing. Which battery fits is determined by the brand, the model and the part number on the battery itself. Check the condition in Windows first with powercfg /batteryreport, and when buying a new battery look at the capacity in Wh and the correct voltage.

When should you replace a laptop battery?

Three signs show it is time to replace the battery. It drains far faster than it used to, the laptop shuts down the moment you unplug the charger, or the battery visibly swells. A swollen lithium-ion battery should be replaced and not kept in use. If Windows itself reports that the battery needs replacing, that is a reliable sign the charge cycles are used up.

Checking the battery in Windows

You check the battery with the built-in command powercfg /batteryreport. Open Command Prompt as administrator, type the command and open the battery-report.html that Windows saves in your user folder. The Installed batteries block shows Design Capacity (as manufactured) and Full Charge Capacity (what the battery still holds today). Divide the second by the first and you have the battery health as a percentage. If you want to go deeper into those numbers, read the explanation of battery life and battery health.

Which battery fits your laptop?

You find the right battery by brand, model and part number. That part number is the key: HP uses codes such as CC03XL or AL08XL, Dell short codes such as RCVVT or 9JRV0, Lenovo numbers such as L20M4P71. You will find it on the label of your current battery, on the underside of the laptop or in the service manual. If you do not know the number, pick your model above and you will see the matching battery straight away.

What to look for in a new battery

Look at capacity, voltage and size. Capacity is given in Wh (watt-hours), sometimes in mAh. A higher capacity means longer use on a single charge, so choose the same value as your old battery or a higher one. The voltage must stay the same, because a battery with the wrong voltage will not charge properly or will not work at all. How long a charge lasts depends on how the laptop is used, the screen brightness and the condition of the battery.

Does the battery differ per brand?

On HP, Dell and Lenovo business models the battery usually sits under the bottom plate, neatly screwed down, and is straightforward to replace yourself. On some thin consumer models the battery is glued into the housing, which makes replacing it more work and often better left to a repair shop.

Making a battery last longer

You extend battery life mainly by avoiding heat and not keeping it charged at 100 percent. According to Battery University (Cadex, BU-808), heat combined with a high state of charge is the main cause of capacity loss in lithium-ion cells. Under normal use a laptop battery still holds around 80 percent of its capacity after a certain number of charge cycles, in practice some 300 to 1000. Keep the charge between 20 and 80 percent for a longer life, and use a charger that belongs to your laptop and charges the battery at the right rate.