{"product_id":"welch-allyn-11720-replacement-battery-36v-750mah-ni-cd","title":"Welch-Allyn 11720 Otoscope Replacement Battery 3.6V 750mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eWelch-Allyn 11720 \/ 11730 Series — 3.6V Ni-Cd Replacement Battery (78904586)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.6V, 750mAh Ni-Cd rechargeable battery for Welch-Allyn diagnostic instruments including the 11720 and 11730 otoscope\/ophthalmoscope handles. It replaces OEM part 78904586. The cell fits the handheld diagnostic handle directly and restores the device to full operating condition.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003e11720 \/ 11730 \/ 18100 \/ 20000 handle compatibility:\u003c\/strong\u003e\n    These handles share the same 3.6V single-cell Ni-Cd format, connector footprint, and charge management circuit. The BMS on each accepts this cell chemistry 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 the Welch-Allyn charge dock and confirmed the charge IC accepted the Ni-Cd chemistry, the BMS completed its verification pass, and the device exited standby without a fault flag.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-use self-test protocol:\u003c\/strong\u003e\n    After fitting this cell, allow the device to complete its full power-on self-test without switching it off mid-sequence. The BMS runs a chemistry verification at startup — interrupting it plants a false battery fault that persists until the next clean reboot.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eLow battery alarm triggering immediately after a confirmed full charge\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe 78904586-format handles use a charge threshold calibrated to the OEM cell's internal resistance profile. A new replacement cell reads slightly outside that window on the first cycle because the Ni-Cd chemistry hasn't yet stabilised its internal resistance. The device interprets this as a weak cell and flags low battery. Run one complete charge-discharge cycle through the Welch-Allyn dock before clinical use. After that first cycle, the BMS learns the cell's actual resistance curve and the alarm clears.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eDevice will not power on after the replacement cell sat in storage\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eNi-Cd cells self-discharge during storage at roughly 1–2% per day. If the cell shipped or sat on a shelf for several weeks, it may have dropped below the BMS recovery threshold — typically around 3.0V for a 3.6V Ni-Cd pack. The device won't power on because the BMS blocks startup below that floor. Place the cell in the Welch-Allyn dock for a full uninterrupted charge before attempting to power on the handle. If the dock charge indicator stalls, confirm dock output voltage is reaching at least 4.5V at the charge contacts.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43381518336090,"sku":"BWCS-WB710MD-1","price":31.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43381518368858,"sku":"BWCS-WB710MD-2","price":36.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43381518401626,"sku":"BWCS-WB710MD-3","price":39.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-WB710MD-1.webp?v=1778901386","url":"https:\/\/batteryweb.com\/products\/welch-allyn-11720-replacement-battery-36v-750mah-ni-cd","provider":"BatteryWeb","version":"1.0","type":"link"}