Short answer: to charge a Shimano Di2 battery on an 11-speed system, connect a dedicated charger to the bar-end or frame junction box, plug the USB-A end into a 5V source, and watch the LED until charging completes. First confirm you have an 11-speed internal battery, because 12-speed systems charge in a completely different way.
If you have just picked up a second-hand Di2 bike, the first job is often the most confusing: there is no charger in the box, and you are not sure whether the bike is 11-speed or 12-speed, or where the charging port even is. This step-by-step guide clears that up.
Step 1: Is your Di2 11-speed or 12-speed?
This matters because the two generations charge in different ways. 11-speed Di2 (Ultegra R8050, Dura-Ace R9150, GRX RX815) uses an internal SM-BTR2 or BT-DN110 battery charged through the junction box. 12-speed Di2 (R9250, R8150, R7150) uses the BT-DN300 battery charged through a port on the rear derailleur with the EW-EC300 cable. If your bike has a bar-end or under-stem junction box, you have the 11-speed style covered by this guide and by the CyclingCharger Di2 internal battery charger (£77.95).
Step 2: Find the junction box and charging port
On 11-speed systems the charging point is the junction box — the small unit (SM-EW90-A/B) usually mounted under the stem, or the bar-end version (EW-RS910) tucked into the end of the handlebar. It has a button, status LEDs and a charging socket behind a rubber cover. If it is a bar-end type, gently prise it out of the handlebar to reach the port.
Step 3: Connect the charger
- Plug the charger into the junction box charging socket until it seats firmly.
- Connect the USB-A end to a 5V source — a UK wall plug, a laptop, or a power bank all work.
- Charge in a dry, ventilated space away from anything flammable.
- Leave it until the LED shows a full charge, then disconnect — do not leave it charging unattended overnight.
- Refit the junction box and confirm the system shifts before your next ride.
Step 4: Read the LED
The charge indicator tells you what is happening: it lights while charging and changes or goes out when the pack is full. A typical full charge from empty takes about 1.5 to 3 hours. If nothing happens, check the cable is fully seated and that your USB source supplies at least 1.0A.
What not to use
Only ever use a Di2-specific charger. Do not improvise with power-tool fast chargers, generic bench or cylindrical-cell chargers, or a USB cable wired to the terminals — the wrong voltage or profile can damage a sealed Di2 pack or void your warranty. For how often to plug in, see our Shimano Di2 battery life guide, and for choosing a unit our Shimano Di2 charger buyer's guide.
The CyclingCharger Di2 charger
The CyclingCharger Di2 internal battery charger makes charging straightforward for 11-speed internal systems. It connects at your SM-EW90-A/B or EW-RS910 junction box, replaces the SM-BCR2 charging function, and charges internal SM-BTR2 and BT-DN110 batteries over USB-A (5.0V in, 8.4V DC 1.0A out) in roughly 1.5 to 3 hours. It weighs 45g, carries UKCA, CE and RoHS marking, and costs £77.95 inc VAT (£64.96 ex VAT) with a 12-month warranty, free tracked UK delivery and 30-day returns — rated 4.8 out of 5 from 256 reviews. It does not fit 12-speed systems.
Bought a used Di2 bike with no charger?
SM-BTR2 and BT-DN110 compatible · UKCA certified · Free UK delivery · £77.95
Frequently asked questions
How do I know if my Di2 is 11-speed or 12-speed?
Look for a junction box. 11-speed Di2 (Ultegra R8050, Dura-Ace R9150, GRX RX815) charges through a bar-end or under-stem junction box. 12-speed Di2 (R9250, R8150, R7150) has no junction box and charges through a port on the rear derailleur with the EW-EC300 cable.
Where is the charging port on an internal Di2 battery?
You do not charge the seat-post battery directly. On 11-speed systems the charging socket is on the junction box — either under the stem (SM-EW90-A/B) or in the end of the handlebar (EW-RS910), behind a small rubber cover.
How long does it take to charge a Di2 battery?
A full charge from empty typically takes about 1.5 to 3 hours. Charging is faster from a wall plug or power bank that supplies at least 1.0A; a low-current USB port will take longer.
Can I use any USB charger for Shimano Di2?
No. You need a Di2-specific charger that connects to the junction box and delivers the correct lithium-ion profile. A standard phone lead cannot connect to the internal battery, and the wrong charger can damage the pack.