Checking Battery Before Buying?

[t2adze]

Hello All

I am going to purchase this battery from this guy, who is selling 3 batteries. His drone got crashed.

I have a question.

1. What should i check before buying the battery? I know how to check the cycles, but what about voltages? What should i pay attention to?

2. Is it better to avoid buying that specific battery that the drone crashed with?

Thanks in advance

 

[Bakersfield Quad]

if you can check them before you buy, that would be best. But if you are ordering them and then checking, well it is a bit of a gamble. If the case is not damaged and there is no deforming of the battery pack, it should be good. But until you put it in and check it, you wont know much about it.

 

[solentlife]

I'd take all 3 !! But then that's me all over. BUT I am not one who likes second hand LiPo's so price has to be really attractive and I would like to have a reliable version of their history.

Can he identify the one that was in the crash ? Do you meet the guy or is it online purchase ? Online - I would be inclined to walk away to be honest as you have no idea if he's telling "porkies" !

Is the price good enough to go for the batterys ? You can buy new under $100 each if you search.

The two not in the crash - why would they be bad ?
The one in the crash - what was reason of crash and what is condition of the pack now ? You could always use that one for bench testing / updates etc. if unsure ...

To check battery - you need a complete flight setup, power all up and then use GO to show battery details ... cycles ... voltage .... etc.

But in reality - because DJI seal up the batterys to stop guys like me getting at them ... you cannot check Internal Resistance etc. which is far more revealing than any GO result.

Nigel

 

[t2adze]

The purchase is not online. I am meeting the guy. He is selling them for 40$ each.
He knows exactly which battery was inserted during crash, because it's still in the drone.

So what do i have to check about voltage and the rest battery details.
What and HOW do i check Only thing i know what to pay attention is - amount of cycles (charges). What else?

 

[solentlife]

You use GO ...

Basically put battery in AC .. power up and go to battery page in menu ....

There's not much else you can do apart from test fly and see how fast the battery goes down.

I would mark the 'crash' one so you know which one. Me ? If it looks in good undamaged condition - I would probably test fly it at low level close range to see how it performs.

Nigel

 

[Mark The Droner]

Check cell balance

Check max mAh

 

[t2adze]

Check cell balance

Check max mAh

what should the value be after which i should mos def not purchase the battery?

 

[Mark The Droner]

You would want the cells balanced and opinions vary what "balanced" means. With a full charge, some say more than 70 mv (.07 v) from the lowest and 2nd lowest cell is where your concerns should begin. I've seen others say 100 mv (.1 v) from the lowest to highest cell is when you should worry. I've seen others say other things.

You should be happy if the max mAh reading (that means with a full charge) is near the rated mAh printed on the battery. With age and use, the max mAh drops naturally so ideally you wouldn't have much of a drop.

You also want to be sure you can't see any swelling in the battery.

Hope this helps

 

[t2adze]

You would want the cells balanced and opinions vary what "balanced" means. With a full charge, some say more than 70 mv (.07 v) from the lowest and 2nd lowest cell is where your concerns should begin. I've seen others say 100 mv (.1 v) from the lowest to highest cell is when you should worry. I've seen others say other things.

You should be happy if the max mAh reading (that means with a full charge) is near the rated mAh printed on the battery. With age and use, the max mAh drops naturally so ideally you wouldn't have much of a drop.

You also want to be sure you can't see any swelling in the battery.

Hope this helps

Great. Thank you

So the battery should be fully charged for me to check, correct?

 

[Erised]

Apart from cycles and cell deviation, for me two of the biggest factors that you can't really check is how he stored and how hard and low he ran down the batteries in each flight. Cell deviation is a deffinite marker but cycles that have been mucked is not apparent (always stored fully charged and drained very low most of the time). Ask the guy how he stored them and to what % he ran them down, now can you really believe it? For these reasons I would alway have trouble trusting any used battery that keeps my craft in the air.

 

[Mark The Droner]

Great. Thank you

So the battery should be fully charged for me to check, correct?

Ideally, yes. Ideally he would fly with it and send you the log

The mAh at any time is a percentage of the max mah relative to the full charge. If you can find out what the current mAh is and what the charge percentage is, you can figure out the max mAh by doing a little math. For example, if it's at 50% charge reading 2240 mAh, and if it's a 4480 mah rated battery, then it's pretty much perfect since it's right where it should be if it was new. Point is, you don't want the max mAh to be too far below the rated mAh. Because, really, it's the mAh you're buying.

 

[t2adze]

Ideally, yes. Ideally he would fly with it and send you the log

The mAh at any time is a percentage of the max mah relative to the full charge. If you can find out what the current mAh is and what the charge percentage is, you can figure out the max mAh by doing a little math. For example, if it's at 50% charge reading 2240 mAh, and if it's a 4480 mah rated battery, then it's pretty much perfect since it's right where it should be if it was new. Point is, you don't want the max mAh to be too far below the rated mAh. Because, really, it's the mAh you're buying.

I see. Thank you!

I have one more question:

My P3A and the 2 batteries that i have are on 1.9FW.
If the battery that this person is selling is updated to the higher FW version, does it mean i will need to update my AC FW as to the higher version as well?

I don't want to update because it works well on 1.9FW and i have bad experience with updateing the drone when nothing is working wrong.

 

[Mark The Droner]

I'm not sure about that.

...anybody...?

 

[solentlife]

No not necessary to manually update because the battery will auto update usually if the FW bin file is there on the card. It only takes a few secs and most people don't realise its happened.
If bin file is not there - it may trigger an update flag in the app.

Nigel

 

[t2adze]

Just talked to the guy.
He said

The battery that is in the drone is the newest. and the crush wasn't that terrible. rolling down the tree type. So i might go for it as well.

What concerned me he says that the rest two are on 1 LED light charged (and added that's how i keep them) - which means he hasn't read the manual at all.
Going to check them in an hour.

Can the battery that is usually stored on 1 LED light be a risk?

 

[umanbean]

Can the battery that is usually stored on 1 LED light be a risk?

That depends on how long and how often it stayed on 1 LED... and 1 is better than fully drained or (for long term storage) fully charged.

From what I've picked up around here, seems like 2 LEDs or 2 with the 3rd blinking is ideal... that would be 37.5 - 62.5%

 

[t2adze]

So, i went and purchased one of his batteries.
I asked him to bring only two, not the one drone was crashed in. (even though that was almost brand new battery)

So he brought two and the funny thing is - BOTH of them, had TOTAL mAH capacity higher then the 2 batteries i do own myself

His battery #1 - was around 90 charges and around 4150mAh
Battery #2 was 74 charges, and was 4047mAh.
(When my batteries 100 and 60 cycles have 3900mAh total capacity left)

So anyway i purchased the one that had less charges but slightly lower mAh capacity.

He was offering me 2nd one for a discount, but i refused. 3 batteries is MORE then enough for me, considering the fact i am planning to sell my p3a before next summer.

Here is the screenshot from my purchase details.

 

[With The Birds]

I would have taken the close to new pack if there was no physical damage and all looked good in the go app. You have still done alright out of the deal.

Will be interesting to see what the flight log reveals after you fly it.

 

[t2adze]

I would have taken the close to new pack if there was no physical damage and all looked good in the go app. You have still done alright out of the deal.

Will be interesting to see what the flight log reveals after you fly it.

I'll be testing it tomorrow and will post results here.

P.S. am thinking maybe to get second one as well. Because after checking my battery #1, the health check of 5 sec holding button, shows 2 leds already. Meaning the battery slowly is becoming risky, correct?
And this one that i purchased, has all 4 blinking on a health check.

 

[solentlife]

I would have taken the lot ... never have enough batterys !!

Nigel