How to troubleshoot Di2 battery drain issues

A well-tuned Di2 system is a joy to ride. It shifts effortlessly and lets you focus on riding the bike. Most riders can go for about 2000-3000 km without having to charge their Di2 battery, but some of us are not so lucky.

As far as Di2 related problems go, unexpected and unwanted battery drain is definitely in the top 5 of hard to troubleshoot issues.

Battery drain causes

There are a couple of variables that can affect battery life. Temperature, the amount and frequency of your rides, wireless unit usage, battery age and shift habits (the front derailleur consumes about 4 times more energy per shift than the rear derailleur).

Besides these common ways of depleting your battery, four potential causes of unexpected and excessive energy consumption are:

• Improper setup
• Update firmware
• Failing cells in the battery
• A fault in a firmware-equipped component (using SM-PCE02)
• A fault in a component without firmware
• Find faults without the SM-PCE02

Diagnose your power issues

There are several ways to diagnose your battery drain issues and most of them can be done at home. Let’s have a look. You will need a couple of tools:

• SM-BCR2 (11-speed Di2) / EW-EC300 (12-speed Di2 battery charger
• TL-EW02 (11-speed Di2) / TL-EW300 (12-speed Di2) electric wire plug tool
• A PC running the latest e-tube project software
• The SM-PCE02 diagnostics tool

Now the last item on this list may be tricky. It is relatively expensive and therefore usually only found at bike shops. You can still do most of the checks without it though, and I’ll describe the SM-PCE02 Di2 battery check process for those of you who do own the device.

#1: Check for any improper setup

First we’ll make sure the bike is set up correctly. Most Di2 installation steps are similar to those of conventional mechanical groupsets, with one big exception: derailleur limit screws. If these are set too tight or restrictive this can cause extra strain and battery usage for both the rear and front derailleurs. Have a look at the front and rear derailleur installation guides for your specific derailleur and double check the limit screws.

Next inspect all the electric wires. Make sure they are not broken, kinked, discolored or deformed. While rare, a malfunctioning electric wire is easily overlooked but can definitely cause unexpected battery drain.

Also, make sure every wire is fully plugged in. Wires that aren't fully seated may appear fine, but can cause all kinds of weird issues that are especially hard to track down.

Wires inside your frame are probably fine, unless they move a lot (when rotating the handlebars for example). Another symptom of damaged wires is having to 'wake up' the system before it'll shift. Note that wireless Di2 systems always need a wake up shift.

While checking the electric wires, use the TL-EW02 (11-speed Di2) / TL-EW300 (12-speed Di2) cable plug tool to double check all connections.

When in doubt, use the tool to unplug and reconnect each component. You should be able to feel and hear the plug snap into the connector.

12-speed Di2

If you are on 12-speed Di2, double check that there is something in the middle port. There absolutely needs to be something plugged into the battery's middle port. If there isn't, that is what could be causing your battery drain issues.

#2: Update component firmware

Sometimes Shimano releases firmware updates that remedy battery issues. Now this does not happen all that often and that firmware is not the most likely cause of unexpected Di2 battery drain, but it can happen. So connect your bike to a Windows computer and check your components for firmware updates.

#3: Check for a faulty battery

In order to make sure it is not the battery itself that is causing you headaches, follow these steps:

10-speed / 11-speed Di2

• Use the battery charger to fully recharge the battery.
• Unplug the battery from the rest of the system. Store it somewhere dry and cool (your shed or room temperature will be fine).
• Wait for 24-48 hours.
• Reconnect the battery and check the battery charge level.

12-speed Di2

• Use the battery charger to fully recharge the battery.
• Disconnect all Di2 wires from the battery.
• Make sure that there is a dummy plug in the battery middle port.
• Store the battery somewhere dry and cool (your shed or room temperature will be fine).
• Wait for 24-48 hours.
• Reinstall the battery and check the battery charge level.

If the battery check indicates the charge level has gone down considerably that means the battery has lost its ability to hold a charge and should be replaced.

#4: Use SM-PCE02 to check components

Shimano must have figured out that battery drain issues are hard to troubleshoot – when they updated the SM-PCE1 linkage device they not only made it smaller and faster, they also added a battery drain check functionality.

This updated device is the SM-PCE02 Linking and Diagnostics device and it can be used to check firmware equipped components for battery issues. It is relatively expensive and most consumers won’t own it. Most bike shops will be able to perform this check for you.

Start by connecting the bike to a Windows Computer. Instead of the SM-BCR2 charger you’ll use the SM-PCE02 device.

Unfortunately, the older SM-PCE1 won’t do – it does not have the battery consumption functionality. Select the correct bicycle type based on your derailleurs and click the ‘Connection Check‘ button.

Select ‘Error Check‘ from the menu on the left side of the screen and make sure you check the ‘Battery Consumption‘ checkbox at the bottom of the window. The software will now check each component for possible battery consumption issues. Once it is done it will tell you which components require further testing. Write these down somewhere and click ‘Complete setup‘.

Now disconnect the bike and use an SM-JC41 junction B and electric wire to connect a single unit at a time.

Click the ‘Change bicycle type‘ button and select Single Unit Connection Mode by clicking the S-shaped e-Tube wire icon at the top right. Shimano’s Single Unit Connection guide can be found on the e-tube project website.

For each unit complete the connection check and then run the ‘Error check‘. Be sure to check the ‘Battery consumption‘ box and begin the check.

If the software finds anything off with the selected component it will let you know. This does not necessarily mean this component is the single cause of your battery issues, but definitely requires further investigation. Disconnect it from the bike and ride the bike for a while. If the battery issues no longer occur that is a good indication you should replace the component.

#5: Last resort – check components without firmware

While you can diagnose firmware-equipped components using the SM-PCE02 and a Windows computer, some components do not have firmware and are relatively dumb. Faults in these components cannot be found through software and you’ll have to spend considerable time eliminating these one by one.

Components without firmware are:

• EW-SD50 Electric Wire
• SM-JC40 external junction B
• SM-JC41 internal junction B
• EW-JC130 Y-splitter wire
• EW-JC200 2-port junction

There are steps you can follow to determine whether or not these components are causing your battery drain. For the electric wires, inspect them and make sure they are not damaged or corroded. Double check the connectors as well.

If there is a suspect electric wire, connect a (known-good) battery to a known-good component (a derailleur for example) using the suspect wire. Leave these three connected overnight and check the battery charge the next day. If it has dropped considerably the electric wire should be replaced. Note that there could be more than one faulty electric wire.

To check a junction box, use two known-good electric wires, a known-good battery and a known-good component. Connect the battery to the junction box using an electric wire and connect the component to the junction box using the other electric wire. Leave these somewhere overnight and check the battery level the next day. Once again, if the battery charge has dropped considerably the component is most likely faulty and in need of replacement.

Stuck? #6: No SM-PCE02? Use a process of elimination

The SM-PCE02 is really useful to check firmware equipped components. Most home users will not own one, simply because it’s rather expensive for home mechanics. This does not mean you cannot check firmware equipped components for battery issues however – you just cannot do it using software.

What I usually do in situations like this is to connect just the bare minimum. You fully charge the battery, and then connect just the battery and the Junction A.

You then wait a day and check the battery charge level. If both the battery and the Junction are good, the battery level will not have dropped at all. Repeat this process, adding another wire and component to the Di2 network. Wait another day, and check the battery level again.

Keep doing this until you've found the culprit. It's a lengthy process, but should eventually lead you to that faulty part or wire.