Simple laptop battery capacity test

Here’s a simple laptop battery test for laptops, notebooks and netbooks based on one basic principle – what goes in, should come out. The simple Laptop Battery test measures actual laptop battery capacity and can be used to rate 2nd hand laptop batteries and (presumably) new laptop batteries.

The simple laptop battery test principle : 
 

The energy stored in a laptop battery  equals the recharge energy needed to reach an empty to full charge.

When a 54Wh laptop battery only requires 25 Wh to fully recharge, the actual capacity of the laptop battery can be expected to be less than 25Wh. Meaning it’s worn down for more than 50 %.

The test precondition is a empty laptop battery.

In this example the simple Laptop Battery Test is used on a DELL latitude D610 laptop battery that lasts for about 70 minutes while browsing the internet.
 

Laptop Battery Test Equipment

Test equipment needed is normal a Watt Meter available at the average DYI or hardware store. This measurement device costs about 20 - 25 US$ on average and can be used for all sorts of other electricity consumption measurements.

 

Laptop Battery Test setup

The DELL latitude D610 laptop battery shows a red blinking light – it’s the sign of a nearly empty laptop battery.

The simple laptop battery test measurement is performed while the DELL Latitude D610 is powered off.
Also a standalone laptop battery charger can be used to measure laptop battery capacity.
 

	Laptop Battery Information in Windows Xp

During measurements the AC power adapter and the bottom side of the laptop warm up indicating power losses. It’s assumed these losses are at least 10%.
 

Laptop battery Test results

The laptop battery charge curve – where actual laptop battery charge power is measured over time:
 

Simple Laptop Battery Test - Measured Laptop Battery Recharge Curve

Shorty after laptop battery charging starts, the power drawn peaks to about 55 Watt and last for about 25 minutes. After charging power reduces to about 5 watts - the laptop battery is reported full.

The Watt meter reported a total of 38 Wh to recharge a 54Wh rated laptop battery over a length of 90 minutes.

A standalone laptop battery charger - bypassing the internal laptop battery charger

It’s safe to extract at least 10 % for losses occurred in the AC adapter and laptop during charging. Actual laptop battery capacity can be expected to be less than 34 Wh, meaning this laptop battery is at least 40 % worn down.
 

Simple Laptop Battery Test limitations

The simple Laptop Battery Test output degrades when actual laptop battery capacity is very low.
Laptop batteries with a short run-time – say 15 minutes – will show a higher capacity rating.

When used on a new laptop battery, actual measured recharge capacity can exceed the rated value because losses occurring in the AC adapter and laptop should also be taken into account.