Is there a way to test for a battery issue, without buying a new battery?

[Xavier]

Ok, so this may be a tricky one, and I wasn't really sure if this is the right place to post this query, but I couldn't really see anywhere else.

My kids have been hassling me to get them an e-bike. Their friends have them, pester pester pester. I cannot afford them though, until recently someone on Marketplace advertised for an Engwe e-bike for sale for only $150.

I was surprised it was so cheap, and my wife called them. They said that the bike was really good, but had suddenly stopped working. They took it to an electrician friend of theirs who looked it over and couldn't see any issues. The electrician thought it was just the bike's battery, but he couldn't be sure.

Unfortunately buying a new battery is $400, and it may not even work. So I could spend $550 and end up with a heap of junk.

With all that background, my question is whether there is a way to test an e-bike to see whether it will work if the battery is new, without buying a new battery first.

The person selling it was very honest and would probably let me test it somehow, if it is possible to do so.

Any help gratefully received.

 

[ElHegpah]

You need a digital volt meter, ideally one with at least two digits after the decimal. Test the battery at the output. Charge battery to indicated full, test. test again in one hour, then a day or two. Find out, FOR CERTAIN, what the fully charged voltage is supposed to be. It is NOT 36, 48, or 52.

Next, rig a load for the battery, light bulb works well, load and test for a couple hours. Carefully record results and report back.

Try SEVERAL TIMES to find out what happened before "suddenly".

 

[briiian]

You need a digital volt meter, ideally one with at least two digits after the decimal. Test the battery at the output. Charge battery to indicated full, test. test again in one hour, then a day or two. Find out, FOR CERTAIN, what the fully charged voltage is supposed to be. It is NOT 36, 48, or 52.

Next, rig a load for the battery, light bulb works well, load and test for a couple hours. Carefully record results and report back.

Try SEVERAL TIMES to find out what happened before "suddenly".

This is hard to do to someone else's bike, in someone else's home.

 

[JerryB]

If the deal sounds too good to be true.....it probably is.....I would be very cautious.

 

[Mysery]

If the owner is willing to let you take the battery maybe you can find a shop, either a bike, electronic or such, to have the battery tested.

 

[Hoggdoc]

Ok, so this may be a tricky one, and I wasn't really sure if this is the right place to post this query, but I couldn't really see anywhere else.

My kids have been hassling me to get them an e-bike. Their friends have them, pester pester pester. I cannot afford them though, until recently someone on Marketplace advertised for an Engwe e-bike for sale for only $150.

I was surprised it was so cheap, and my wife called them. They said that the bike was really good, but had suddenly stopped working. They took it to an electrician friend of theirs who looked it over and couldn't see any issues. The electrician thought it was just the bike's battery, but he couldn't be sure.

Unfortunately buying a new battery is $400, and it may not even work. So I could spend $550 and end up with a heap of junk.

With all that background, my question is whether there is a way to test an e-bike to see whether it will work if the battery is new, without buying a new battery first.

The person selling it was very honest and would probably let me test it somehow, if it is possible to do so.

Any help gratefully received.

First of all how old are your kids, some locations have laws preventing younger from legally from riding e bikes. They can be dangerous in some kids hands. As for the $150 deal you found unless you are a skilled technical person that knows and is comfortable with figuring out problems that could exist on e bikes I would run the other way.

 

[ElHegpah]

There is no real test, other than what I have described, to tell you the true state of a battery. Even then, it is a rough guess.

Charge and test, wait 10-20 minutes and test, ride for 10-20 minutes and test, this you can do and it will tell you a little bit.

Generally, no used battery is worth over $50.00.

If the battery remains way low on voltage, then that is at least part of the problem but any competent electrician would have determined that.

Look closely for loose wires, and I mean trace every single one, examine for cuts, look HARD, disconnect the ebrake levers connection to the controller, check the battery connections and see if you can borrow a similar one from somebody, OK not likely but not too many other things to test without a battery. If the battery will hold full or close to full voltage, then it should at least turn on and maybe move a bit. If it does not turn on at all, check the voltage again.

A bad battery can appear fully charged but drop rapidly and severely in voltage under any usage such that the system will shut off. The voltage will also quickly rebound when the load is removed, this is a bit tricky to test. More load will mean more drop and less complete recovery.

Back to that competent electrician.

Not likely they will tell you, but SOMETHING happened to the bike.

Also, when they say "stopped working", does that mean it does not move, does not light up the display at all, or lights up briefly and goes blank, or will stay lit up until you hit the throttle, then immediately dies, or goes 5-10 feet and dies, or goes for 2-3 minutes and dies, lotsa variations here.
There may also be lights on the battery itself seperate from the display, and sometimes these will display differently ON the bike as opposed to OFF the bike. Also not uncommon AT ALL for the on-bike charging port to be defective but a (hopefully separate) charging port on the battery DOES work.

"It does not work" is not very helpful, but an amazingly common trouble report.

 

[Freddy1]

My advice, forget that particular bike. It is likely an unpowered bit of kit not worth the hassle of fixing or spending money on it. Put your $400 for a new battery toward something new with a decent spec (voltage, battery size, motor wattage). A relatively inexpensive Chinese bike with decent specs can be found.

 

[BretCahill]

There is no real test, other than what I have described, to tell you the true state of a battery. Even then, it is a rough guess.

Charge and test, wait 10-20 minutes and test, ride for 10-20 minutes and test, this you can do and it will tell you a little bit.

Generally, no used battery is worth over $50.00.

If the battery remains way low on voltage, then that is at least part of the problem but any competent electrician would have determined that.

Look closely for loose wires, and I mean trace every single one, examine for cuts, look HARD, disconnect the ebrake levers connection to the controller, check the battery connections and see if you can borrow a similar one from somebody, OK not likely but not too many other things to test without a battery. If the battery will hold full or close to full voltage, then it should at least turn on and maybe move a bit. If it does not turn on at all, check the voltage again.

A bad battery can appear fully charged but drop rapidly and severely in voltage under any usage such that the system will shut off. The voltage will also quickly rebound when the load is removed, this is a bit tricky to test. More load will mean more drop and less complete recovery.

Back to that competent electrician.

Not likely they will tell you, but SOMETHING happened to the bike.

Also, when they say "stopped working", does that mean it does not move, does not light up the display at all, or lights up briefly and goes blank, or will stay lit up until you hit the throttle, then immediately dies, or goes 5-10 feet and dies, or goes for 2-3 minutes and dies, lotsa variations here.
There may also be lights on the battery itself seperate from the display, and sometimes these will display differently ON the bike as opposed to OFF the bike. Also not uncommon AT ALL for the on-bike charging port to be defective but a (hopefully separate) charging port on the battery DOES work.

"It does not work" is not very helpful, but an amazingly common trouble report.

Last fall I made a ~20 - 25 Amp dummy load to test the cell bank [no BMS] I had just rebuilt. It wasn't holding much charge. A novice spot welder I was looking for hot spots on the nickel strip welds.

This dummy load wasn't very linear but was cheap and did the job.

I taped off the bottom of a 1 1/2" PVC tube ~ 2' long and put two al angles in shimmed apart by electrical tape, about half a mm thick, as electrodes. I then filled it with pulverized charcoal. Two or 3 of the teeth whitening charcoal powder at Dollar Tree may be enough and you don't get dirty banging on grill charcoal. Then partially fill with water. Add salt and water until you get to 20 Amps. This is not ohmic so you need some way to measure current.

Steam will boil out after 10 seconds. I managed to hang in there for a minute before shutting down -- this rig made me nervous -- but the battery seemed OK.

It worked for about 5 months with a 50% increase in range. Recently the battery sag started to be 5 v under load. Everything shuts down over 10 Amps.

I have checked the battery and it looks ok. I will try the dummy load again today. If I don't get any info I will try used battery.

 

[Scoti]

This saved me typing a lot of info .

Note
If your not competent enough don't try this .

ttps://evbaron.com/how-to-test-an-e-bike-battery-in-5-quick-steps/

 

[BretCahill]

A more advanced test for charge for 2 half way good batteries with the same nominal voltage:

Charge one battery up a couple volts more than the other. Connect them in parallel with a amp meter to measure the current. The battery with the higher voltage should charge the lower voltage battery. I use fuses for this work.

After an hour or so when the current goes to zero and the voltages equilibrate see which voltage moved the most.

I used a 3p x 10s at 38.5v to partially charge a 4p x 10s at 37v. Current started out at 1.5 A and I quit at 0.22 A.

Both voltages ended up at 37.6. The 3p moved -0.9v and the 4p moved +0.6v. The 4p stores 50% more charge than the 3p per volt when you would expect it to be only 33% more since all cells of both batteries were the same.

The 3p still has the BMS but that shouldn't matter much if at all.