Sony VAIO VGN-FZ Series - Manual (Page 121)

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Precautions
❑ If, after fully charging the battery pack, the battery power is still low, the battery pack may be reaching the end of its life
and should be replaced.
❑ You do not need to discharge the battery pack before recharging.
❑ If you have not used the battery pack for a considerable amount of time, recharge the battery pack.