About this replacement
Xhorse VVDI Key Tool Max Programming Device — 3.7V Li-Polymer Replacement Battery (AHT655060)
This is a 3.7V, 2500mAh Li-Polymer replacement battery for the Xhorse VVDI Key Tool Max Programming Device. It fits the AHT655060 cell slot directly and restores full device operation when the original cell has degraded. Dimensions are 62.00 x 50.00 x 6.30mm — confirm these against your existing cell before ordering.
- VVDI Key Tool Max compatibility: The Key Tool Max uses a single Li-Polymer cell on a 3.7V rail with a dedicated BMS that monitors charge state and communicates with the device firmware. A cell that drifts below spec triggers a low-voltage lockout, so voltage and physical dimensions must match exactly.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a VVDI Key Tool Max unit. The BMS accepted the cell without error flags, and charge termination triggered correctly at 4.2V with no thermal anomaly.
- Export vehicle profiles before swapping the battery: The VVDI Key Tool Max stores session data in RAM backed by the main battery. Pull all saved key profiles and vehicle records to the Xhorse app or a PC via USB before disconnecting the old cell — this data is not retained once power is cut.
Why the VVDI Key Tool Max refuses to boot after a battery swap
The Key Tool Max firmware checks cell voltage at startup and will not complete the boot sequence if it reads below approximately 3.0V. A brand-new Li-Polymer cell ships at a storage charge of around 3.6–3.8V, which is usually enough to boot — but if the cell has sat in a warehouse for several months, voltage can drift lower. If the device shows nothing on screen after the swap, connect the OEM charger and leave it for 30–45 minutes before attempting to power on. Do not attempt to boot the device repeatedly from a deeply discharged state, as the BMS will lock out the cell to prevent damage.
Wireless connection dropping mid-key programming session
The VVDI Key Tool Max uses Bluetooth for communication with the Xhorse app during key generation and transponder cloning. BLE transmission draws a short burst of higher current, and when the battery cell is aged or partially discharged, voltage momentarily sags enough to cause the wireless stack to reset. This appears as a sudden disconnection mid-session, even when the battery indicator still shows two or three bars. If you see this symptom with the old cell, it confirms the cell is no longer holding voltage under load — replace the cell and ensure it is charged above 3.9V before starting a programming session.