Kit Builders - test your Battery befor 30 days expires


Well-Known Member
I finally got my battery, shipped to a friend near my summer camp, home to maintenance base. 48 v 15 AH, should put out 3 amps for 5 hours. Display been blanking out on me after 13 miles at 10 mph, Battery reads okay (>55 v) shortly afterwards with meter but didn't have meter hooked up during failure. I have to watch the road when riding, not a meter. You can't plan the outage to be at a time when you are looking at the meter.
So I hooked up three 5 ohm 200 W resistors in series to make a 4 amp load at 58 v, the charger cutoff voltage. Put a meter in parallel. See picture. FHD0031.JPG Battery is in silver frame lower right to be bolted securely to the bike.
Bought resistors (dark brown) from surplus house for $6 each to test PA amplifiers with. Any 15 ohm 200 W setup could work, even an assemblage of 5 watt resistors. See for details on building amp test load bank.
Charge the battery, connect to resistors, flip the switch, the battery collapses to 18v. Fail.
31 day warranty via e-bay expired summer 2017. In sun-ebike favor, I did store the battery eight feet underground in a tornado shelter during the winter, which got down to -8 deg F. That could have been the problem. I still suspect the infamous level of quality from a country I usually don't buy from may also have been the problem. All ebike parts come that country, IMHO.
So I'm out $320. Still way cheaper than a branded bike, that no model in a show room will fit me. See the thread begging for a demonstration of a 17" frame Stromer in stock under buy and sell forum . That frame might fit me, but you have to pay for it before you can try it out. ***** them. I'll build something on a frame I know, heavy steel so I don't bend it with a motor in it. Next battery is a Luna, getting shipped to my city maintenance base and will be tested the first week before installation.
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Well-Known Member
I don't doubt that you got a bad battery, but I am wondering about the results. Seem inconsistent. If it is dropping to 18V on a 4 A load, how did you manage to ride 13 miles earlier?

In addition, battery BMS shouldn't let the voltage go much under 33 volts, if that low. It ought to open up the pass transistors and you get no voltage.


Well-Known Member
I typically ride at 50-100 W which is 1 to 2 amp, unless I'm going up a steep hill. Display tended to blank out once I enterred area of steep hills. Thanks for explanation of what is "normal". Since two batteries had a motor that the display was blanking out on after 10-13 miles, I thought the fault was the motor. Until this test. May still be the motor/controller, too. First battery charged up from 46 to 58 volts in 10 minutes on a 2.5 amp charger, a clear sign that only one or two of the 14 stacks was in circuit when I received it