{"product_id":"samsung-sph-a820-replacement-battery-37v-750mah-li-ion","title":"Samsung SPH-A820 Replacement Battery 3.7V 750mAh Li-ion","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eSamsung SPH-A820 \/ SPH-A840 \/ PM-A840 — 3.7V Li-ion Replacement Battery\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.7V, 750mAh (2.78Wh) Li-ion replacement battery for the Samsung SPH-A820, SPH-A840, and PM-A840 flip phones. These handsets launched on Sprint's early 2000s network and share a common battery form factor across the three model numbers. If the original cell no longer holds a charge, this unit restores the phone to normal operating condition.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eSPH-A820, SPH-A840, and PM-A840 compatibility:\u003c\/strong\u003e\n    All three models share the same battery bay dimensions (65.84 × 41.75 × 7.35mm), voltage rail, and connector pinout. One battery fits all three without modification.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this cell through charge and discharge on compatible hardware. The BMS held the charge cutoff correctly at 4.2V and the low-voltage protection tripped at the expected threshold, with no thermal event during the charge phase.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    After installing this cell, run one full discharge-to-charge cycle before relying on the battery percentage indicator. The phone's fuel gauge IC is calibrated to the old cell's discharge curve. Without a full cycle, the percentage reading will be inaccurate and the phone may shut down at an unexpected charge level.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the SPH-A820 shuts down suddenly at 20–30% after a battery swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens because the phone's fuel gauge IC still tracks the discharge curve of the old, degraded cell. When the new cell hits a voltage point the gauge associates with 20–30% on the old curve, the phone interprets it as a critical low and triggers a protective shutdown. The actual cell still has capacity — the gauge just doesn't know it yet. One complete discharge cycle, letting the phone run down to automatic shutdown and then charging uninterrupted to 100%, resets the coulomb counter against the new cell's real curve.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003ePhone not powering on after the replacement battery sat in storage\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eLi-ion cells self-discharge in storage. If this battery dropped below approximately 2.5V per cell before installation, the BMS will have entered a deep-discharge lockout state and the phone will show no response when you press the power button. Connect the phone to a charger and leave it for 20–30 minutes without pressing anything — the charge IC needs to push a low recovery current into the cell before the BMS will re-initialise. Once the BMS releases lockout, the charging indicator will appear. If the screen stays blank past 45 minutes on charge, check that the charger is outputting at least 5V.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43409457578074,"sku":"BWCS-SMA840SL-1","price":23.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43409457610842,"sku":"BWCS-SMA840SL-2","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43409457643610,"sku":"BWCS-SMA840SL-3","price":29.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-SMA840SL-1.webp?v=1779579767","url":"https:\/\/batteryweb.com\/products\/samsung-sph-a820-replacement-battery-37v-750mah-li-ion","provider":"BatteryWeb","version":"1.0","type":"link"}