HP Compaq Series Hardware Manual page 37

Battery Packs
To remove a MultiBay battery pack, turn the notebook upside
down. Then slide and hold the MultiBay release latch 1 as you
pull the battery pack 2 from the MultiBay.
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CAUTION: To prevent damage to the MultiBay when no device is in
the MultiBay, insert the weight saver to protect the bay opening. The
weight saver can be inserted or removed while the notebook is on, off,
in Standby, or in Hibernation.
Hardware Guide 3–5