About this replacement
Panasonic EY3653 / EY3654 Series — 7.2V Ni-MH Replacement Battery (EY9065)
This is a 7.2V, 2100mAh Ni-MH replacement battery for the Panasonic EY3653, EY3653CQ, EY3654, and EY3654CQ cordless drill/drivers. It replaces OEM part numbers EY9065, EY9066B, BCP-EY9065, and PA-724. The battery slots into the same bay as the original and connects to the same contact rail.
- EY3653 and EY3654 compatibility: Both models run the same 7.2V battery bay and contact layout. The BMS handshake on each platform expects the same voltage window and thermistor signal, so one battery covers all four variants without modification.
- Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the EY3653 platform. The BMS accepted the pack without fault codes, held the voltage rail steady under load, and the thermistor circuit reported correctly throughout the cycle.
- Ni-MH cycling on compact drills: Avoid leaving this battery on a trickle charger overnight after the charge cycle completes. Panasonic's EY9065-format packs are prone to voltage depression from sustained overcharge — pull it from the charger once the indicator shows full.
BMS cutoff on motor-start inrush with the EY3653
When you pull the trigger on a compact drill, the motor draws a brief inrush current that can be three to five times the steady running current. On a 7.2V Ni-MH pack, if the cells are cold or partially discharged, internal resistance climbs and the voltage rail dips sharply at that inrush spike. The BMS reads this as an overcurrent event and trips the protection circuit before the motor reaches running speed. Let the battery warm to room temperature and ensure it is above 6.5V before use to keep the BMS from tripping on trigger pull.
Charger not recognising a new pack after storage
Ni-MH cells self-discharge during storage, and if a pack sits long enough, cell voltage drops below the threshold the Panasonic charger uses to confirm a valid battery. The charger sees the low voltage as a fault rather than a discharged pack and refuses to start a charge cycle. Connect the battery to the charger and leave it for 15 minutes — some chargers apply a brief wake-up pulse before switching to full charge mode. If the charger still shows a fault, check that the contact rail on the battery reads at least 5.5V with a multimeter; anything above that voltage should allow the charger to initialise.