Sony PCG-GRX580P - Manual (Page 35)

Using a Second Battery Pack
You can purchase a second rechargeable battery pack. With two battery packs, you can extend the time that you use your
notebook with battery power. When using two battery packs, the battery pack you insert first charges first. The battery
pack you insert second begins charging when the first battery pack is 85 percent full. You can monitor which battery pack is
charging by observing the battery indicators.
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