Sony Clie PEG-UX40 UP553 Replacement Battery 3.7V 850mAh
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Sony Clie PEG-UX40 UP553 Replacement Battery 3.7V 850mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.
🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Sony Clie PEG-UX40 UP553 Replacement Battery 3.7V 850mAh - is backordered and will ship as soon as it is back in stock.
Voltage
3.7V
Amp
850mAh
Sony Clie PEG-UX40 / PEG-UX50 — 3.7V Li-Polymer Replacement Battery (UP553)
This is a 3.7V, 850mAh Li-Polymer replacement for the Sony Clie PEG-UX40 and PEG-UX50 PDAs. Both units share the same battery footprint and BMS handshake, making this a direct fit across the pair. Original UP553 cells in these early-2000s devices have typically lost 40–60% of their rated capacity by now.
- PEG-UX40 and PEG-UX50 compatibility: Both Clie models use the same flat Li-Polymer cell format, the same flex connector, and the same Palm OS power management stack. The BMS negotiation is identical across both, so one cell covers the pair without modification.
- Bench tested on actual hardware: We ran this cell through the Clie's charge cycle and confirmed BMS handshake at 3.7V nominal. The protection circuit tripped correctly at low-voltage cutoff, and charge acceptance reached full 850mAh capacity within spec.
- Sync before you swap: The Clie PEG-UX40 and UX50 hold application data, contacts, and open files in volatile RAM powered directly by the main battery. Pull the battery without first syncing to the desktop HotSync software and that data is gone — there is no secondary backup cell in these units.
Why the Clie PEG-UX40 loses all data when the battery goes flat
The PEG-UX40 runs Palm OS from ROM, but all user data — contacts, calendar entries, memos, installed applications — lives in SRAM. That SRAM needs continuous battery voltage to hold its contents. When the cell drops below the BMS cutoff threshold, even briefly, the SRAM loses power and wipes. There is no onboard flash storage backing up that data between syncs. The fix is a full HotSync to your desktop before voltage drops that low — not after.
Clie PEG-UX40 stuck on boot screen after new battery install
A freshly shipped Li-Polymer cell typically arrives at storage voltage — around 3.6V — which is below the minimum the Clie's Palm OS boot sequence needs to complete. The device starts initialising, hits the power floor, and stalls on the boot screen or resets in a loop. Do not assume the battery is faulty. Connect to the AC adapter and let the cell charge for at least 30 minutes before attempting to power on. A stable 3.7V or above clears the stall and lets the boot sequence finish normally.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Sony
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Li-Polymer
- Battery Type: Li-Polymer
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
My Clie PEG-UX40 lost all my contacts and calendar after I swapped the battery — is there any way to get them back?
Almost certainly not from the device itself. The PEG-UX40 stores all user data in SRAM, which requires continuous battery voltage to retain its contents — once the old cell was removed and voltage dropped to zero, that memory wiped. If you ran HotSync before the swap, your data is intact on the desktop and restores on the next sync. If not, the data is gone from the device. Always HotSync immediately before any battery work.
The PEG-UX50 keeps restarting on its own after the new battery was installed — what's causing it?
This is almost always a voltage issue, not a faulty cell. A new Li-Polymer battery ships at partial charge, and if the Clie's BMS reads the incoming voltage as marginal, the device boots, draws a spike of current, voltage sags below the cutoff threshold, and the unit resets. Leave it on the charger for 45 minutes before powering on. Once the cell reaches a stable 3.7V, the restart loop stops.
Wireless sync via Bluetooth drops constantly on the PEG-UX50 since the battery swap — why?
The Bluetooth radio on the UX50 is sensitive to voltage sag under load. If the replacement cell hasn't reached a full charge, the radio draws more current than the cell can sustain at low state-of-charge, and the voltage dips enough to cause the radio to drop. Run a full charge cycle first — confirmed full when the charging indicator clears — then test the Bluetooth sync again. If drops continue after a full charge, check that the flex connector is fully seated; a loose connection creates the same voltage instability.
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