Lenovo ThinkPad T420s User Review Battery Life, Heat and Noise

May 26, 2011 by John Ratsey Reads (291,128)
Editor's Rating

Ratings Breakdown (1-10)

    • Software & Support
    • 9
    • Upgrade Capabilities
    • 8
    • Usability
    • 9
    • Design
    • 8
    • Performance
    • 9
    • Features
    • 8
    • Price/Value Rating
    • 8
    • Total Score:
    • 8.43
    • Rating 1 to 10, top score 10

Heat and Noise
The cooling system of the T420s should be capable of dissipating the heat from the version equipped with a dedicated GPU. Keeping a Core i5 processor with Intel integrated graphics cool should therefore not be a challenge. However, given the noise created by the fan in response to sustained full CPU load, together with a maximum CPU temperature of around 90°C there, does not appear to leave much thermal headroom. The cooling fan appears to have three speeds: A quiet 2,000rpm, a slightly audible 4,000rpm and a noisy 4,700rpm. The thermal rules in the BIOS leave scope for improvement: Once the fan is running, then it is reluctant to stop; even with the computer on idle and a CPU temperature of 45°C. On one occasion, it continued to run at the maximum speed until I shut down the computer.

If users wish to avoid this much fan noise, then they can use Lenovo?s Power Manager opt to sacrifice performance in favour of a quieter life. Power Manager provides a visual indication of the effect of changes in the power settings.

Under heavy stress of benchmarking the system, the case temperatures were a maximum of  90°F on the keyboard-side and slightly hotter on the bottom with a peak of 102°F near the CPU fan. This is getting warm, but the location means that user contact is unlikely even if the computer is being used on a lap.

Maximum temperatures (°F) during benchmarking:

Battery and Power Consumption
Purchasers can order either a 65W or a 90W PSU. My measurements at the mains socket indicate that 65W is sufficient for a T420s with the Intel graphics and I prefer the smaller power supply for reduced baggage.

The T420s has a standard 6-cell battery rated at 44Whr. This is only about 2/3rds of the capacity of the 6-cell batteries used in many notebooks. The small cells presumably reflect a desire to minimise weight and thickness. The main battery can be supplemented by using a second UltraBay battery to add about 70% to the overall capacity.

If an UltraBay battery is present, then the computer will deplete that first. The user could then swap the battery for another one. However, when charging the batteries the computer will recharge the main battery first.

Battery Life
The Arrandale CPUs represented a step forwards in performance and a step backwards in power efficiency. Intel have rectified the latter with the new CPUs (the cynic in me believes that the incremental improvements are part of a marketing strategy). The i5-2520M CPU will run at only 800MHz under light load which helps reduce the idle power consumption.

Battery run time depends on the usage conditions and display brightness. Under light usage (such as working on a Word document with other programs closed) with the display at half brightness (anything lower is getting very dim) my T420s has a power drain of 7.5W to 8W. Under moderate usage (such as a web browser with many tabs open) the power drain is 10W to 12W. What do these numbers mean? Divide the battery capacity by the power drain and you get the potential run time. That means about 5 hours, perhaps a bit more, with light usage and 3 to 4 hours of moderate usage using the main battery only, and 5 to 8 hours with an UltraBay battery to help out.

Lenovo?s Power Manager appears to have some optimism since, with both batteries on board it has forecast 10 hours. However, I haven?t had the patience to prove it right. Instead, I have bought a second UltraBay battery (a previous generation one which is slightly lower capacity but easier to find) for the occasions when I?m short of mains power.

Lenovo have achieved the objective of a thinner, lighter version of the T420. However, it comes with two noticeable compromises: A lower capacity battery; and a smaller cooling system which is barely up to the task. The 16:9 aspect ratio display is another less satisfactory feature. I?m getting used to it, but my reaction to turning my Dell E6410 on is the delight of looking at the bigger display. The quality of the display also leaves something to be desired and it appears that Lenovo could have done more to optimise settings to get the best from the available panels. However, to quote an old English proverb: ?You can?t make a silk purse out of a sow?s ear.?

So, am I happy with my purchase? Overall, yes. I?ll get used to the clattery keyboard because it is otherwise pleasant to use. I?ll rarely be needing sustained CPU usage that makes the fan scream (and I can turn on some music to drown the keyboard and noise). And now I?ve managed to tweak the display settings, it looks OK until I look at another, better screen. Finally, I was wanting less weight and in that area the T420s meets the requirements although the UltraBay battery starts to erode the weight margin. This is the first time I?ve bought a Thinkpad. It?s too early to predict if I will repeat the experience but I have invested in the 3 year on-site warranty in case I encounter any problems.


  • Light weight for display size
  • ThinkPad classic looks and build quality
  • ThinkPad keyboard
  • Full feature set including USB 3.0
  • Good pointing device options


  • Poor quality display for price range
  • Low capacity battery
  • Most ports are at the back
  • Uses 7mm storage devices with capacity limit



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