Batteries

Warning: do not buy cheap replacement Nokia batteries from ebay or other such sites. Most of these batteries are fakes and come with a much lower capacity than advertised. The tablets use lithium-ion batteries, which have specific requirements for care to maintain optimal battery longevity.

  • No memory. "Li-ion batteries do not suffer from the memory effect. They also have a low self-discharge rate of approximately 5% per month, compared with over 30% per month in nickel metal hydride batteries and 10% per month in nickel cadmium batteries."
  • Capacity loss is a function of number of full-discharge cycles since manufacturing, and other stress factors, including over-/under-voltage, over-current, and over-/under-temperature. "a battery stored inside a poorly ventilated laptop may be subject to a prolonged exposure to much higher temperatures than 25 °C, which will significantly shorten its life."
  • Heat and cold shortens battery lifespan (heat buildup can be reduced with proper ventilation). "a battery stored inside a poorly ventilated laptop may be subject to a prolonged exposure to much higher temperatures than 25 °C, which will significantly shorten its life."
  • Heat affects capacity loss during storage. "Different storage temperatures produce different loss results: 6% loss at 0 °C/32 °F, 20% at 25 °C/77 °F, and 35% at 40 °C/104 °F. When stored at 40% charge level, these figures are reduced to 2%, 4%, 15% at 0, 25 and 40 degrees Celsius respectively."
  • Voltage range is from 3.0V (discharged) to 4.2V (charged), with 3.7V being nominal.
  • Guidelines to extend battery life
    • Stay 40-60% charged for storage - around 3.6-3.8V. "Unlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a longer time, they should be brought to a charge level of around 40%. Lithium-ion batteries should never be "deep-cycled" like Ni-Cd batteries"
    • Stay cool. "Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly."
  • Only buy new batteries when you need them.

Checking your battery status

There is much more information available about the battery than the charge indicator icon. To get a more precise description of the battery's charge, type

lshal | grep percentage

in the xterminal (Open xterm with Ctrl-Shift-x). The lshal (list hardware abstraction layer) command returns a long printout of information about the hardware. Grep is a linux user command that searches input for a specific string and prints the line that it is found in.

The percentage that is returned is relative to the fullest charge the battery has ever sustained, so it will be less than 100 even after recharging, and the highest value it can reach will decrease over time as the battery wears.(See the comments.)