Battery testing / multimeter help

adri

New Member
Region
Canada
Hey guys, I came across someone with a broken version of my ebike for sale, with lots of upgraded parts, and two batteries, for $1,000.

I want that bike's upgraded parts. The batteries alone could resell for about $500 each. Can I use a multimeter to determine which of the three batteries I should keep? If so, should I be testing voltage, ohms, or resistance?

From what I've read, the more resistance a battery has, the worse off it is. Does that mean I should get rid of the batteries with the most resistance and keepthe one with the least, or is there more to it than that?

Thanks!
 

Timpo

Well-Known Member
Hey guys, I came across someone with a broken version of my ebike for sale, with lots of upgraded parts, and two batteries, for $1,000.

I want that bike's upgraded parts. The batteries alone could resell for about $500 each. Can I use a multimeter to determine which of the three batteries I should keep? If so, should I be testing voltage, ohms, or resistance?

From what I've read, the more resistance a battery has, the worse off it is. Does that mean I should get rid of the batteries with the most resistance and keepthe one with the least, or is there more to it than that?

Thanks!
Multimeter won't tell you much.

You will need a battery capacity testor, to see exactly how many Ah (or Wh) it can hold.
Even that, it may not give you exact cycles you have left, but will give you better idea than multimter.
 

tomjasz

Well-Known Member
Well running the battery under stress, like full throttle can tell you a lot. Checking with a multimeter can confirm your display accuracy. Does the battery sag under use? A cheap power meter can give you more but I’d be happy with running at max power and noting how deep the battery sags. I’ve got an old 20Ah triangle pack. If I watch the watts it’s sucking and stay around 500w I can squeeze miles out of it, but hit the throttle and hit 1100 and sure enough the LVC low voltage cutout shuts my motor down.
 

6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
One way to look for the best battery is to road test each one. Fully charge them all and ride 10 miles on the same route using the same PAS & pedal effort. Then check with a multimeter. The one with the highest voltage is likely the best.

This won't tell all though but it will give you a rough idea of how they compare to each other.
 

Bitmugger

Active Member
Region
Canada
Basic way to check which is "better" but without a capacity meter

Charge each battery fully and make sure voltage is 54.6v or as close to it as possible (assuming 48v bike).
If you can wire a basic household light bulb socket to the battery do that and put in an old style 100w incandescent light bulb (not an LED one). That should consume about 40w of juice and will drain the battery slowly, let it run and check it every 1-2 hours to see which battery drains first. (It'll take hours and hours to fully drain at such a low rate). Do not use a CFL or LED bulb.
 

harryS

Well-Known Member
Must be a super nice bike if people are willing to pay $500 for a used battery. My new ones don't even cost that much. I assume you're going to buy this bike?

I feel the best way to decide which battery is good is to charge them all up and ride til the bike shuts down. The range you get will be the main factor, but there's also performance. Some batteries will seem to work fine til you get down to 50%, and then they shut down quick like Tomjacz' triangle pack.

You're correct about the resistance. You can have high series resistance along with high AH capacity. That means the battery will last a long time if you were just running the lights, or going really slow, but if you blip the throttle, the voltage sag is so high that it shuts down the battery. So take your time to evaluate your batteries, if they are that saleable.

Congrats on a nice find.
 

Timpo

Well-Known Member
One way to look for the best battery is to road test each one. Fully charge them all and ride 10 miles on the same route using the same PAS & pedal effort. Then check with a multimeter. The one with the highest voltage is likely the best.

This won't tell all though but it will give you a rough idea of how they compare to each other.
Yeah that's why I said battery capacity tester would be the best bet.
Multimeter will only tell you the percentage of power left, it won't tell you the capacity.

For example, if 10A battery has 9.4A capacity, well it probably has lots of life left.
Whereas if you only get 6.8A capacity, it's probably reaching the end of its life.
 

Timpo

Well-Known Member
Must be a super nice bike if people are willing to pay $500 for a used battery. My new ones don't even cost that much. I assume you're going to buy this bike?

I feel the best way to decide which battery is good is to charge them all up and ride til the bike shuts down. The range you get will be the main factor, but there's also performance. Some batteries will seem to work fine til you get down to 50%, and then they shut down quick like Tomjacz' triangle pack.

You're correct about the resistance. You can have high series resistance along with high AH capacity. That means the battery will last a long time if you were just running the lights, or going really slow, but if you blip the throttle, the voltage sag is so high that it shuts down the battery. So take your time to evaluate your batteries, if they are that saleable.

Congrats on a nice find.
Oh I didn't see that, good catch.
$500 for a used battery is quite a bit.
 

Timpo

Well-Known Member
Hey guys, I came across someone with a broken version of my ebike for sale, with lots of upgraded parts, and two batteries, for $1,000.

I want that bike's upgraded parts. The batteries alone could resell for about $500 each. Can I use a multimeter to determine which of the three batteries I should keep? If so, should I be testing voltage, ohms, or resistance?

From what I've read, the more resistance a battery has, the worse off it is. Does that mean I should get rid of the batteries with the most resistance and keepthe one with the least, or is there more to it than that?

Thanks!
What kind of bike is it?
More importantly, what kind of battery does it have?
 

tomjasz

Well-Known Member
Yeah that's why I said battery capacity tester would be the best bet.
Multimeter will only tell you the percentage of power left, it won't tell you the capacity.

For example, if 10A battery has 9.4A capacity, well it probably has lots of life left.
Whereas if you only get 6.8A capacity, it's probably reaching the end of its life.
And riders with a multimeter, taking a hard ride as I explained above get to the same place. Unfortunately many riders are ill equipped to sort connectors and use a RC Wattmeter. If the battery is decent he'll have very little sag. !!KISS!!

And yes, $500 for a used battery is goofy!
 

adri

New Member
Region
Canada
Sorry, should have specified, I'm talking CAD, I'm assuming you guys are talking USD. $500 CAD is about $315 USD.

I have a battery load tester, and a multimeter, but I don't have a battery capacity tester. Is it the same thing as a load tester?
 

harryS

Well-Known Member
If you want to start counting electrons, buy an RC wattmeter for about $13-15 USD. If you put it in between your battery and your charger, which is easy with some adapter plugs, you can measure how many Watt-hours or amp-hours go back into your battery when your recharge. That;s always going to be a little higher than what came out, but you can look at battery capacity with it.

The other way is to put it between the battery and the controller, but that's not always possible unless you have the wires available. Then you can measure power used by the bike, as well as peak current.

They have some accuracy issues, but for $15, you only need relative numbers.


P4240137.JPG
 

Bitmugger

Active Member
Region
Canada
Sorry, should have specified, I'm talking CAD, I'm assuming you guys are talking USD. $500 CAD is about $315 USD.

I have a battery load tester, and a multimeter, but I don't have a battery capacity tester. Is it the same thing as a load tester?

What do you mean a "battery load tester". Can you share a pic or description of it? Might be of use.

A 48v battery 13ah brand new in Canada from Leon Cycle Canada is $250 shipped to give you a sense of competing battery prices. That battery will be using Panasonic cells inside so it's top quality.
 

adri

New Member
Region
Canada
What do you mean a "battery load tester". Can you share a pic or description of it? Might be of use.

A 48v battery 13ah brand new in Canada from Leon Cycle Canada is $250 shipped to give you a sense of competing battery prices. That battery will be using Panasonic cells inside so it's top quality.

Sure. I come from motorcycles. Electric vehicles are very, very, new to me. I'm struggling.

But I've been around motorcycles for 15ish years so I'm pretty nifty there. This is a battery load tester, it's used for testing (typically automotive) batteries:

stalwart-inspection-tools-hw6000014-64_1000.jpg


Costive to positive, negative to negative. Then nothing happens, it just tells you the voltage.

After that, you flip the load switch or hold the button, and it places a controlled load against the battery, and continues monitoring the battery's voltage, in order to see how the battery performs.

Based on the battery's performance under load (for up to 10 seconds), it shows you a rating of either GOOD, OK, or BAD.

Note: You should only test the battery once it's been fully charged, otherwise you're likely to get a false BAD or false OK. Shady car/motorcycle mechanic shops will do this to tell you your battery needs replacing when it may only needs recharging.

This isn't made for ebike batteries though, I'm assuming, as it's designed for 6 and 12 volt batteries. But here is a link if you just want to learn more about them. I've used one pretty much identical to this for almost a decade. It will outlive me: https://amzn.to/3GxG5RL

Ideally I would love something plug and play like this. I hit a switch, and I can see how the battery performs with the touch of a button, repeat on all three batteries, and that's it.

Can someone plz give me a link to the tool everyone here is recommending? I'm in over my head and might abandon this project haha.
 

tomjasz

Well-Known Member
Fellas! Seriously? You're making this harder than it needs to be. RIDE!! Test the battery under a riding load. Hammer that throttle. No need to turn this into a difficult process. Or buy more devices.

If you must, go with ----> HarryS <---- and his response he's in the top three builders here.
 
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Bitmugger

Active Member
Region
Canada
Sure. I come from motorcycles. Electric vehicles are very, very, new to me. I'm struggling.

But I've been around motorcycles for 15ish years so I'm pretty nifty there. This is a battery load tester, it's used for testing (typically automotive) batteries:

stalwart-inspection-tools-hw6000014-64_1000.jpg


Costive to positive, negative to negative. Then nothing happens, it just tells you the voltage.

After that, you flip the load switch or hold the button, and it places a controlled load against the battery, and continues monitoring the battery's voltage, in order to see how the battery performs.

Based on the battery's performance under load (for up to 10 seconds), it shows you a rating of either GOOD, OK, or BAD.

Note: You should only test the battery once it's been fully charged, otherwise you're likely to get a false BAD or false OK. Shady car/motorcycle mechanic shops will do this to tell you your battery needs replacing when it may only needs recharging.

This isn't made for ebike batteries though, I'm assuming, as it's designed for 6 and 12 volt batteries. But here is a link if you just want to learn more about them. I've used one pretty much identical to this for almost a decade. It will outlive me: https://amzn.to/3GxG5RL

Ideally I would love something plug and play like this. I hit a switch, and I can see how the battery performs with the touch of a button, repeat on all three batteries, and that's it.

Can someone plz give me a link to the tool everyone here is recommending? I'm in over my head and might abandon this project haha.

Thanks for the info. That device isn't of use though for your 48v lithium ion batteries just due to voltage differences and that good/bad/weak gauge is designed for lead acid batteries. Here's a link to a proper capacity testing meter that is cheap (requires some wiring).


It doesn't require a separate shunt and is easy to wire up (2 wires in from battery, 2 wires out to a load). To use it find a suitable load (I use light bulbs) and charge the battery fully and hook it up and let it drain to empty. The meter will indicate the total Watt-Hours which is the capacity of your battery.
 

6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
Sure. I come from motorcycles. Electric vehicles are very, very, new to me. I'm struggling.

But I've been around motorcycles for 15ish years so I'm pretty nifty there. This is a battery load tester, it's used for testing (typically automotive) batteries:

stalwart-inspection-tools-hw6000014-64_1000.jpg


Costive to positive, negative to negative. Then nothing happens, it just tells you the voltage.

After that, you flip the load switch or hold the button, and it places a controlled load against the battery, and continues monitoring the battery's voltage, in order to see how the battery performs.

Based on the battery's performance under load (for up to 10 seconds), it shows you a rating of either GOOD, OK, or BAD.

Note: You should only test the battery once it's been fully charged, otherwise you're likely to get a false BAD or false OK. Shady car/motorcycle mechanic shops will do this to tell you your battery needs replacing when it may only needs recharging.

This isn't made for ebike batteries though, I'm assuming, as it's designed for 6 and 12 volt batteries. But here is a link if you just want to learn more about them. I've used one pretty much identical to this for almost a decade. It will outlive me: https://amzn.to/3GxG5RL

Ideally I would love something plug and play like this. I hit a switch, and I can see how the battery performs with the touch of a button, repeat on all three batteries, and that's it.

Can someone plz give me a link to the tool everyone here is recommending? I'm in over my head and might abandon this project haha.
I would be very careful using this tester on an e-bike battery. It puts a heavy load on the battery and measures the voltage drop. It is designed for automotive use and the load, usually 100 amps, could blow the battery fuse or damage the battery itself.
 

adri

New Member
Region
Canada
Yes I would definitely not recommend using that for anything other than a 6V or 12V battery it was designed for as mentioned. Just love the simplicity of the tool and someone asked about it so I wanted to share some info