Sony LSPX-S1 Help Manual page 11

If the ON/STANDBY (power) indicator is not lit up while connected to an AC outlet while the speaker is off, the battery is fully charged. Once the
battery is fully charged, it will not be charged furthermore even if the speaker is kept connected to an AC outlet.
Note
Even if you do not intend to use the speaker for a long time, charge the battery to its full capacity once every six months to maintain its
performance.
4-580-768-11(2) Copyright 2016 Sony Corporation
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