Complete power loss with 15 seconds


10 µW
Sep 30, 2023
Just bought a used (Costco Urban Ryder), did a really short test ride... all seemed good. 500 watt 8-Fun motor with 48 volt, 13 amp/hour battery.

Got it home and found when I use throttle and open it up or go to assist level 2 or 3, it loses all power, LCD display goes out, all is dead. Seems if I just plod along in Level 1 it will go farther.

When it dies, I cycle the key off/on, will work again but then the same results of it losing power. Battery is currently sitting about 51.8 volts Powers up properly, I checked and double checked all the connections, all seems tight and good. Thought maybe a bad connection and going over bumps would cause this but it happens while testing the bike in a stationary position (my apartment).

So I ran a little test, disconnected the rear brake motor cut-out switch and with rear wheel off the ground, started throttling it and runs great with no load, hooked up my multi-meter, battery is about 47-48 volts while running (no brake), applied the rear brake to simulate a load, volts drop a couple to maybe 43 - 44, I apply more brake (not too much) and within maybe 10-15 seconds all power goes out. When power dies, battery drops to about 12.5 to 12.7 volts and sort of drops slowly from there, I cycle key off/on and it's back to 51.7 volts. Did this 7 or 8 times with the same results. The controller was made in 2014, bike was sold brand new last summer, I bought it yesterday with 200 kms (120 miles) on it. I don't know a lot about e-bikes so would this be a battery, motor or controller issue? Motor sounds quiet and good throughout testing/riding.
Battery problem--most likely one or more cells is no longer capable enough; too high a resistance or too low a capacity. It's usually called a balance problem, or unbalanced cells. ****

If this is the case, you may be able to help the battery do a bit more than it does now (but not work like it was new) by leaving it on the charger at least overnight ; it can take much much longer (days or even weeks) if the imbalance is extreme. I recommend only leaving it charging when you can physically be there to monitor it, because every battery of every kind always has some form of fire risk during charging (not much, but it's there, and a battery already known to have a problem of one kind may be at more risk).

It is not a repair, or any form of permanent fix; the only way ot do that is to replace the low-capability cells with new ones (which will then be the high-capability cells and the rest will now be lesser than those). But it can let you use the pack more and under higher loads than while imbalanced, at least until it gets imbalanced again, or ages enough to simply not be able to do what you want.

**** All balance means is that the voltages are all identical at whatever state of charge (SoC) the pack is at the moment of testing. Usually that is at full charge (top balance), sometimes at empty (bottom balance), and the BMS in all of these ebike batteries use the former to tell when it is full.
So I took apart the 48v batt, have been looking on Amazon for a replacement "pack" to swap out the insides in my current battery case, but not seeing the greatest of reviews on a lot of these "off-shore" batteries. Anyone had luck with a particular brand from Amazon... thinking that maybe buying Samsung or Panasonic might be the wise move.... any ideas or suggestions?
Haven't seen much on amazon, ebay, etc that is worth getting (most of them I woudln't consider safe, some of them are outrageous lies).

I don't have direct experience with any good sellers other than a very old pack from EM3EV (of a kind they don't make anymore), but others have had good modern experience with them, and with, and a few other places. There are a number of recent (past few months) threads discussing good sellers / vendors if you poke around a bit, with useful info.
Thanks for the feedback! Greatly appreciated! Ended up cracking the wallet and buying a 48v with Samsung, been out the last couple days, having warm weather so all's good! Cheers
if you've taken the battery apart and are still able to test it on the bike. do the same test again until it fails and check each cell group.
If your quick enough you might see 1 (or more ) groups is low & when you charge, 1 (or more) goes high. It can be used as a pointer to the problem cell group you have.