Clock battery
Confirm the battery type before desoldering anything. Some PlayStation 2 boards carry a soldered cell rather than a simple coin holder. Never short the battery terminals, and discharge static from yourself before touching the board.
The PlayStation 2 keeps its internal clock running with a small backup battery, the timekeeper cell. When it dies the console forgets the date and time whenever it is unplugged, and some software that checks the clock can behave oddly. The battery has no effect on saved games, which live on the memory card, so this is purely about keeping the clock alive.
How to tell it has failed
- symptom Clock resets every time the unit loses power
- symptom The system always boots to the clock-setting screen
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Identify the cellOpen the console and locate the round coin battery on the main board. Note whether it sits in a removable holder or is soldered down with tabs.
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Remove the old batterySlide a holder-mounted cell out gently. For a tabbed cell, desolder the tabs cleanly so the pads are not lifted or bridged.
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Fit the replacementInstall a fresh cell of the same type, observing polarity. A tabbed replacement should be soldered quickly to avoid overheating the battery.
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Reassemble and set the clockClose the shell, power on, and set the date and time. Unplug briefly and check that the clock now survives the power loss.
Low priority repair
A dead timekeeper battery is mostly a convenience issue. If everything else works, you can keep using the console and replace the cell whenever it is convenient.