Ebike loses all power in about 15-20 seconds...

Old Guy New Bike

New Member
Did a short test ride and bought a used (Costco Urban Ryder) yesterday... 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 runs for about 10-15 seconds then 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 for 15 - 20 seconds but then the same results of it losing power. Battery is 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 also happens when I tested 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 48 volts while running (no brake), applied the rear brake a little to simulate a load, volts drop a couple to maybe 44 - 45 volts, I apply more brake (not too much) and within maybe 10-15 seconds all power goes out including LCD display. When power dies, battery (multi-meter) reads about 12.7 volts and continues to drop slowly from there, if I cycle the key off/on, it's back to 51.7 volts. I 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. Motor sounds quiet and good throughout testing/riding. Nothing gets hot while testing (other than the brake... grin). I don't know a lot about e-bikes so would this be a battery, motor or controller issue?
Battery. It's most likely unbalanced inside. There are many knowledgeable articles on the web about this problem. Google unbalanced ebike batteries if you want to learn more. I've seen this on a couple of batteries. The max charge on a 48V battery should be 54.6V, but these charged only to around 53V, Then they would shut off at 48-50V, even though the normal shutoff is 40V.
Once in a great while, if you have a compatible battery, a long extended 2-3 day charge can resolve the issue. Do it in a safe place, as it's not longer good practice to leave batteries on extended charge unsupervised. However, most low cost ebike batteries cannot equalize themselves like this,
Good thinking on the load test! I like that.

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?
Is this the bike?

The picture doesn't show the battery clearly. I'm guessing it's the venerable SIlverfish case with 48V. They come apart if you're a dogged DIY person and there is a rectangular block of cells inside, but I don't think you can buy them pre-assembled. You might find a blue shrinkwrapped 48V battery that could fit, but those are often of dubioud quality.

There's room though for 65 cells in that green wrapper. Mine only had 40 as it was a 36V battery so almost 1/5 of the space was just empy slots. , I was going to upgrade mine with new cells from 36V to 48V, but I gave the bike away.
Given you probably paid $400 or less for the bike, I don't think you will like the advice to pay $500 for a high quality battery. There are a lot of them for sale for around $250 of indifferent quality, with chinese cells. Some might last 4 years. Others just past the warranty period.. Depends on how cheap the cells.

Various vendors with name brand cells

Cheapo Vendor. Difference is that quality LG, Samsung, Panasonic cells cost about $5-6 retail, and the bttery needs 52 to 65 of them. These batteies use 89 cent cells.