Ebike La Paz

While electric bicycle batteries are generally reliable, some are still left wondering: why is my ebike battery not charging? Or not powering the motor at all. Recently, I encountered two separate batteries that were not working. 

In both cases, the symptoms were nearly identical, and standard troubleshooting methods didn’t solve the issue. Both ebike batteries are sitting in my workshop, hoping I can find a way to bring them back to life while the owners ride their perfectly good ebikes with new batteries. 

Here’s a breakdown of what happened, why each test was performed, and what might actually be going wrong inside the battery. If you can help me figure these issues out, I would appreciate any help you can offer in the comments.

The Situation

Both batteries showed up to my shop unable to turn on their ebikes or charge to full capacity using their chargers. A quick analysis also show these identical behaviors:

• They would not power the ebike
• There was no voltage at the discharge port
• They would not charge, and the charger stayed green, meaning it was not sensing a voltage.

To confirm the issue wasn’t with the ebike itself, I connected a different battery of the same voltage. The ebike worked perfectly.

This confirmed the problem was entirely within the battery. So I investigated further.

Theory For Why Is My Ebike Battery Not Charging: BMS Shutdown

The most common cause of a “dead” ebike battery is the Battery Management System (BMS) shutting down. The BMS should protect the battery from:

• Over-discharge
• Overcharge
• Short circuits
• Cell imbalance

When it shuts down, it can completely cut off output, making the battery appear dead. I have suffered this issue with my LiFePO4 solar batteries, and successfully woken their BMSs up, so I thought to try the same techniques with ebike batteries.

What I Tried

I attempted to “jump start” the battery by connecting it to another battery of the same voltage. In theory, this powers the BMS enough to start working again, allowing charging and powering on the ebike.

Why this test:
The BMS is off to protect the cells. A small current pushes it to start working again, protecting the cells from damage.

Result:
No change. The battery remained unresponsive.

I tried connecting voltage to multiple contact points on each battery, and there was no response. Maybe I will try with a smaller voltage, but so far this repair has not worked.

Testing For Why Won’t Ebike Battery Charge: Checking For Charger Issue

When connecting the charger, the charge indicator light stays green, instead of turning red, indicating that the battery is charged. This shows the battery is full, or the charger does not sense voltage from the battery, like it is not connected.

Why this matters:
If the charger doesn’t detect the battery, it will not send current. This suggests a break in the circuit or that the BMS is not allowing current flow.

I tried several different chargers with the same voltage and charging from different contact points. There was never a response from the battery, so the charger is not the problem.

Testing Voltage at the Output

Using a multimeter, I checked the discharge port. It gave me almost 0 volts, sometimes like 1 or two volts, but I interpreted this result as 0 volts. 

I tried charging through the discharge ports with a modified ebike charger. The charger would turn red, indicating charging, but when I disconnected the charge and checked the voltage, I got a reading of about 30 volts, which quickly diminished to 0 volts again.

If the cells are healthy but the BMS is blocking output, there may still be voltage inside the pack, but not at the terminals. This test made me think that the BMS is shutting off the connection from the charging and discharging ports, but I am not sure.

Checking the Ebike Battery Fuses

I inspected the fuses and they appeared intact. I also attempted to charge through the fuse wiring.

There are two fuses, one for charging and one for discharging. I disconnected and reconnected both of the fuses. 

Also, I tried charging through these two connections and got no results. This would make me think there could be a break between the cells, which I have not investigated fully because it involved opening the battery more, which is more dangerous and could ruin the battery.

What This Likely Means

At this point, the issue appears to be internal. The most likely causes include:

1. BMS Failure

The BMS itself may be defective, not just temporarily shut down.

Possible issues:

• Damaged internal components
• Failed switching elements (MOSFETs)
• Complete blockage of current flow

This explains the lack of charging and discharging.

2. Internal Connection Failure

There may be a physical break inside the battery pack.

Examples:

• Loose nickel strip
• Broken weld
• Disconnected cell group

This would explain the brief voltage reading followed by a drop to zero.

3. Cell Group Failure

If one group of cells has failed or dropped too low, the BMS may prevent operation entirely.

This is more common in older batteries, but one of these batteries was only three months old, suggesting possible manufacturing issues.

4. BMS Not Receiving Cell Data

If the balance leads are disconnected, the BMS may not detect the cells and shut down as a safety precaution.

What It’s Not

Based on testing, the following can be ruled out:

• The ebike itself
• The charger
• External connectors or wiring

Where to Look Next

The issue is almost certainly inside the battery pack.

Further steps would include:

• Opening the battery case
• Measuring voltage across individual cell groups
• Inspecting internal wiring and welds
• Testing continuity through the BMS

This process carries risk, as lithium batteries can be dangerous if mishandled. With both batteries, the owners opted to buy new batteries rather than investigate further.

Why Is My Ebike Battery Not Charging? A Mystery To Be Solved Another Day

The ebike industry in La Paz is still small. We do not have the capacity to fix all issues, and it remains easier to buy new batteries than repair them at this point.

But, Ebike La Paz promises to keep learning, and one day we will repair all ebike related problems. If you have an issue, please contact us and we may have a solution, or at least we can learn together the best next step.

Thanks for reading!