power failure problem Gunai gn29 ebike 750w


New member
Local time
8:26 AM
Nov 12, 2023
Hi, I'm from France so sorry for my bad english :) I've had a gunai gn29 for 1 month, it's a ebike with 750 watts brushless motor and 48V battery. The first use I charged the bike normally the battery indicated 54.4v on the screen display. I was able to ride about 35 km on assistance 2 so 25km/h with a few climbs. After that, during a climb, the bike shut down completely, screen and battery, impossible to switch back on using the button on the display. I had to take the battery out and put it back in to turn the screen back on. The display shows 47 volts and when I'm on a climb I see the voltage drop to 37 volts and the bike shuts down completely. Same thing with assistance 4 and 5 on the flat when the battery gets to around 47 volts.
The second time, it happened after a 40 km ride.
What is the cause of the problem? what can I test to find out if it's the battery, controller or display?
Thank you


Well-known member
Local time
1:26 AM
Aug 30, 2023
I would think minimum battery voltage protection cutoff, should be around 40-41 volts on a 48 volt setup. Maybe the battery cutoff voltage was never setup in the display.


Active member
Local time
2:26 AM
May 30, 2023
54.4V is 0.2V too low. Not huge, and if the battery were a year or two old, I wouldn't worry about it. However, this battery is brand new.
0.2V could be just an inaccurate meter. If spread across multiple parallel groups, not such a big deal. HOWEVER, if this 0.2V is ALL in one, single parallel group, in a brand-new battery, could indicate a defective cell or bad weld, or similar. A cell which will not charge fully is often also a cell which will sag in voltage dramatically under load.

"impossible to switch on using button on display", BUT, R & R the battery, NO CONNECTION TO CHARGER, and the switch works. BMS has NOT been reset by a charge, but the controller has been reset by removing power. Controller LVC has been activated.

Incorrect LVC settings are common, however the voltage displayed before cutoff is in the correct range.

CRITICAL INFORMATION NEEDED - "when I'm on a climb" - THIS IS THE EVENT THAT CREATES THE SHUTDOWN!!!! TWICE!! How LONG, in distance, How much TIME, in minutes, and How much CLIMB, in feet of altitude, is involved ????????? Rough estimates are OK. There are MOUNTAINS, in France. Also need an estimate of your level of pedaling effort during the climb.

Also need to know EXACTLY how much weight is being carried on the bike.

BOTH shutoff events occurred during a climb. This is a high load event. HOW HIGH that load is, is a critically important piece of data.

The voltage drop is pretty steep, though this depends on the climb data. You could have a seriously defective battery which may represent a clear and present danger to yourself and those around you. Take care to store the bike far away from any flammable materials, outside the home.

The testing needed will involve opening the battery, and accessing the sense wire connector on the BMS itself. Tedious, you will need a DVM with a readout containing at least two decimal places, just one is not good enough. I would investigate warranty coverage first, also test the output of the fully charged battery, and multiple times during a long ride. The display voltage could be off significantly, and 47V, that is 3.6V per cell, is at the point where voltage sag starts to really accelerate. The amount of stored power is not linear, this is well over half-depleted.

EDIT: Need the Amp-hour rating of your battery.