Riester 10691 3.5V XL Replacement Battery 3400mAh Li-ion

Riester 3.5V XL Series — 3.7V Li-ion Replacement Battery (10691)

This is a 3.7V, 3400mAh lithium-ion battery replacing OEM part number 10691. It fits Riester 3.5V XL, Led Li-Ion, C Handles, and 3.5 Ri Accu C Type Handle diagnostic instruments — the otoscopes and ophthalmoscopes used in clinical examination. Voltage and capacity match the original cell exactly.

• 3.5V XL and C Handle compatibility: These models share a common 3.7V lithium-ion cell format, the same connector pinout, and a BMS handshake that validates cell chemistry at startup. Any cell outside the correct voltage window fails that check immediately.
• Bench tested on actual hardware: We cycled this cell through the Riester power-on self-test sequence. The BMS accepted the cell on first insertion, completed its verification pass, and held charge under the instrument's LED and lamp load without a false-low alarm.
• Post-swap self-test protocol: After installing this cell, let the device complete its full power-on self-test without switching it off mid-sequence. Riester instruments run a BMS verification at startup — interrupting it plants a false battery fault that persists until the next clean reboot.

Why the Riester XL flags low battery immediately after a confirmed full charge

The Riester BMS stores a capacity baseline from the previous cell and compares it against the new one on first use. A fresh cell that hasn't completed a full charge-discharge cycle doesn't yet match that baseline, so the instrument interprets the delta as a fault. This is not a defective battery. Run one complete charge-discharge cycle before clinical use and the BMS recalibrates to the new cell's actual capacity curve.

Device will not power on after the replacement cell sat in storage

Lithium-ion cells self-discharge during storage. If this battery has been sitting unused, its resting voltage may have dropped below the Riester BMS recovery threshold — typically around 2.5V per cell. The instrument won't attempt to wake a cell it reads as critically discharged. Charge the battery in its cradle for at least 30 minutes before trying to power on the device; the charge IC needs to bring the cell above the wake threshold before the BMS will allow a start sequence.