The 9 cell thinkpad battery 57 extends the run time of the w541 t440p t540p w540 l440 and l540 systems on average the battery lasts for an incredible 100 watt hours each one is rechargeable and uses over discharge protection to ensure power flows securely advanced lithium ion li ion technology is used to combine efficiency and performance making this battery ideal for replacing ageing systems or for use as a convenient spare each one is safeguarded with a chip which authenticates w