(there are many guides on how to do this on the internet). BMW E90/91/92/93 as well as many BMW key fobs from the early 2000's. BMW had a different shape pcb leg mount put on the there batteries (which you cant buy) but this just requires a little modification.
eBay
5Pcs Mini L1154F Battery Case Battery Storage Box Battery Holder For AG13 LR44 Coin Cell Battery Compartment Battery Holder
Aliexpress UK
Panasonic VL2020 3V Lithium Coin Cell Button Battery High Capacity 20Ah. Model: VL2020. Key Features Compact & Lightweight: Easy to fit into small electronics.
eBay
40pcs CR2032 Battery Holder Coin Button Cell Battery Holder Case CR2032 Battery Holder 3V CR2032 Button Coin Cell Battery Holder
Aliexpress UK
BMW E90/91/92/93 as well as many BMW key fobs from the early 2000's. (there are many guides on how to do this on the internet). BMW E39 and E46 keys (Commonly Known as Diamond Keys). BMW had a different shape pcb leg mount put on the there batteries (which you cant buy) but this just requires a little modification.
eBay
DIY Battery Holder 1/2/3/4/8 Slots D Size Battery Holder Cell with Wires Durable Battery Holder Case Rechargeable Battery Case
Aliexpress UK
eBay
1.55V 3V Button Cell Battery Power Tester Electronic Tester Battery Meter Button Cell Battery Tester Measuring Instrument
Aliexpress UK
Panasonic OEM battery. The battery will require soldering to the remote board.
eBay
3.7V 3200mAh LiPo Battery Drone Backup Battery UAV Battery For E88 E99 E99S F185 Mini Drone Battery RC Quadcopter Parts Battery
Aliexpress UK
1xVL2020 Battery. Battery Capacity: 50mAh. Battery Technology: Lithium Vanadium Pentoxide. Battery Size Code:2020. For Chrysler. For Citroen. For Hyundai. For Jaguar.
eBay
EEMB 5~100PCS CR1632 3V Button Cell Battery 120mAh Lithium Battery Non-Rechargeable Cell Batteries
Aliexpress UK
Panasonic VL2020 3V Lithium Coin Cell Button Battery High Capacity 20Ah. Model: VL2020. Compact & Lightweight: Easy to fit into small electronics. Key Features.
eBay
BT-168 BT1 Digital Battery Tester LCD Display 9V 1.5V Battery Button Battery lithium Battery Power Voltage Battery Indicator
Aliexpress UK
Panasonic VL2020 3V Lithium Coin Cell Button Battery High Capacity 20Ah. Model: VL2020. Key Features Compact & Lightweight: Easy to fit into small electronics.
eBay
18650 Lithium Battery Holder4x5 Cell Spacer Battery Plastic Holder Bracket, Cell Spacer for DIY Fixed Battery (1pcs/5pcs/10pcs)
Aliexpress UK