GPSMAP 64 series / GPSMAP 64x series - Installing a NiMH Battery Pack
NiMH Battery Pack
Amazon.com: Gomadic Unique Portable Rechargeable Battery Pack Designed for The Garmin VIRB Ultra 30 - High Capacity Charger That fits in Your Pocket : Electronics
BP-696i: 7.2volt 4000mAh Ni-MH replacement insert for Garmin GPSMAP696, 596
GPSMAP 64 series / GPSMAP 64x series - Charging the Battery Pack
Amazon.com: Garmin Rechargeable NiMH Battery for GPSMAP 64s/Oregon 600 Series GPS : Electronics