Battery-killing firmware bug?

[The Editor]

Sounds like you may have just dodged the bullet on the firmware bug. Apparently the automatic self-discharge is very slow so that it does not generate excessive heat. I'd bet that if you had waited longer your batteries would have discharged until they were dead.

I would recommend keeping an eye on them anyway to be sure they were not damaged by over discharging.

No, you are misunderstanding how the discharge function works.
The self discharge only takes the pack down to circa 3.86v per cell after a pre determined time (1-10 days set by the user).
If left unattended they DO NOT continue to discharge - they go into a hibernation state of extremely low quiescent current and must be 'woken up' from this stage in order to accept a charge again. What you experienced by the sound of it is NOT an over discharge condition but a failure to wake from hibernate.

 

[tfmkevin]

No, you are misunderstanding how the discharge function works.
The self discharge only takes the pack down to circa 3.86v per cell after a pre determined time (1-10 days set by the user).
If left unattended they DO NOT continue to discharge - they go into a hibernation state of extremely low quiescent current and must be 'woken up' from this stage in order to accept a charge again. What you experienced by the sound of it is NOT an over discharge condition but a failure to wake from hibernate.

You are describing how the discharge function is SUPPOSED to work. And, that is the way it worked - except in the firmware versions I installed last fall. That version of the firmware has a bug that causes the self discharge to continue slowly discharging past the 3.86v per cell target - right down to "dead".

DJI just fixed that bug in the most recent version of the firmware. They documented it in the release notes:

"Major Updates
1. Improved encryption to enhance transmission security. Aircraft and Remote Controller must be upgraded to prevent unlinking.
2. Fixed issue of batteries over-discharging when stored for extended periods of time (over 90 days)."
​

My batteries are most definitely over-discharged. I took the tops off and measured individual cell voltages. Individual cells were 0.7-0.9V - definitely destroyed. You can't bring a LiPo cell back from discharge below 1V.

Just as an experiment, I disconnected the balancing plug and carefully charged them back to a voltage of 4.1V per cell. That would allow the battery board to boot and operate temporarily, but the cells quickly sagged back to less than 1V when the charging source was removed.

 

[tfmkevin]

Here is a complete description of the issue:
Rock, Paper, Firmware

 

[The Editor]

Here is a complete description of the issue:
Rock, Paper, Firmware

Kevin,

Can I suggest you write an email to Ed Windham at DJI? at [email protected]
(maybe with a link to your article?). The batteries should NOT have done this!

Ed heads up customer service for North America - mention I suggested you get in touch with him.

 

[tfmkevin]

I will do that. I don't know your name other than "The Editor"...

 

[The Editor]

I will do that. I don't know your name other than "The Editor"...

PM sent.

 

[Mad_angler1]

I can't be continuing self discharge as that would kill the packs in a week or so, I suspect the issue was the packs not entering deep hibernation under curtain conditions and draining them down very slow.

Ed is a good guy and will do his best to help.

But they have admitted this one on the update release notes so they should cover it, if all the cells are drained it can only be a FW issue as they don't discharge them selves in that amount of time.

 

[tfmkevin]

I can't be continuing self discharge as that would kill the packs in a week or so, I suspect the issue was the packs not entering deep hibernation under curtain conditions and draining them down very slow.

Ed is a good guy and will do his best to help.

But they have admitted this one on the update release notes so they should cover it, if all the cells are drained it can only be a FW issue as they don't discharge them selves in that amount of time.

I agree completely. The MCU that takes care of the batteries has to be hibernated or it would very slowly drain them. There has to be some kind of microwatt-level watcher that minds the system in hibernate mode. (Obviously I haven't really tried to reverse-engineer their board).

 

[tfmkevin]

Just an update on this. I emailed Ed Windham at DJI as suggested above. It's been 12 days and there has been no reply.

I've moved on - I bought two new TB48s to get me back into the air.

Nice trick to sell more batteries, I guess - write some code that destroys batteries when they are stored for the winter, force people to install it, then when they discover the problem and contact support tell them "Here's the link to buy yourself some new batteries."

 

[clingermac]

Battery problems like we have on these smart batteries must be intentional. They are smart enough to die for a number of reason and they are smarter than we are because we continue to buy more misery. I have 3 batteries with a minimum of 90% left. The last one was put in the day of the update. I received it to replace the two that went dead. I got it charged it, put it in the inspire and had the center two leds flashing very fast before it went dark. There is good reason why every new quad operates on a different voltage. I have a Vision 2+ with three batteries, a Phantom 3 with 1 battery ( I wised up), and an Inspire 1 with 7 batteries (3 of which show no signs of life)and 2 remotes. Regarding the latest one DJI told me to send it in and they would have a look. Watch e-bay all of my DJI quads will be on there soon. My next order of business will be to find a good quad that will take readily available batteries that cost less than $200.00 each. I am so full of DJI.

 

[AllanM]

What about the possibility of batteries discharging themselves in storage prior to customer despatch?
I just bought two TB48's from an ebay supplier. One was perfect, arrived 50% other arrived nearly dead. First shows 5700 available other shows 5643 after one charge each. Every one of my dozen or so batteries has shown 5700 on the first charge, except this one which arrived flat.

??

 

[The Editor]

What about the possibility of batteries discharging themselves in storage prior to customer despatch?
I just bought two TB48's from an ebay supplier. One was perfect, arrived 50% other arrived nearly dead. First shows 5700 available other shows 5643 after one charge each. Every one of my dozen or so batteries has shown 5700 on the first charge, except this one which arrived flat.

??

It's perfectly possible for a battery to lose some capacity between rolling off the production line and arriving at the end user.
Lipos actually deteriorate over time whether they are used or not. You can expect even a perfectly stored pack to lose around 2-3% capacity a year.

 

[AllanM]

It's perfectly possible for a battery to lose some capacity between rolling off the production line and arriving at the end user.
Lipos actually deteriorate over time whether they are used or not. You can expect even a perfectly stored pack to lose around 2-3% capacity a year.

Please re-read my post.

 

[The Editor]

Please re-read my post.

Yes they can discharge during transit/sitting on a dealers shelf/in a transit container etc.
That can ALSO lose capacity without even being used.
You need to find out the manufacturing date of the pack. Of course, what you will never know is how it has been treated (temperature wise) before it got to you.
Sorry - does that not answer your question?

 

[AllanM]

Yes they can discharge during transit/sitting on a dealers shelf/in a transit container etc.
That can ALSO lose capacity without even being used.
You need to find out the manufacturing date of the pack. Of course, what you will never know is how it has been treated (temperature wise) before it got to you.
Sorry - does that not answer your question?

The post was with reference to the OP.
I was insinuating that the firmware bug which existed previously could be responsible for the low charge (basically flat) state of the battery when I received it, and was really looking for comment on that aspect.

Yes, we all know Lipos, as with all batteries may discharge over time for various reasons, but I have never received a new battery in this condition before.
I had several batteries left over 4 months (the rainy season (;>) ) and they did not lose substantial charge, I left them at 50% and that's about where they were in March.

 

[The Editor]

The post was with reference to the OP.
I was insinuating that the firmware bug which existed previously could be responsible for the low charge (basically flat) state of the battery when I received it, and was really looking for comment on that aspect.

Yes, we all know Lipos, as with all batteries may discharge over time for various reasons, but I have never received a new battery in this condition before.
I had several batteries left over 4 months (the rainy season (;>) ) and they did not lose substantial charge, I left them at 50% and that's about where they were in March.

Ahh, gotcha...... As it is a new battery you might also try removing the top and disconnecting the logic board plug for an hour (the reset trick). You may actually find this 'recovers' your lost 57mAh.

 

[AllanM]

Ahh, gotcha...... As it is a new battery you might also try removing the top and disconnecting the logic board plug for an hour (the reset trick). You may actually find this 'recovers' your lost 57mAh.

Going slightly off topic (;>) Forgetting the reason (FW or otherwise), do I accept the battery 'as is' or simply send it back as faulty on arrival?

It's not the 57mAh I'm concerned about, it's the overall health of a new battery. It wasn't perfect when I received it - if it was a TV it would go back.
I appreciate I could to the reset (which I've done before with some success), but loathed to on a brand new battery.

 

[tfmkevin]

If my theories about the firmware bug are correct, a new battery that was originally shipped with the buggy firmware from the factory, and which was then stored for several months before it was purchased, could be DOA because of the bug.

Batteries shipped with other versions of firmware, or put into service and updated without long-term storage should be OK.

Just my theory...

Kevin

 

[The Editor]

Going slightly off topic (;>) Forgetting the reason (FW or otherwise), do I accept the battery 'as is' or simply send it back as faulty on arrival?

It's not the 57mAh I'm concerned about, it's the overall health of a new battery. It wasn't perfect when I received it - if it was a TV it would go back.
I appreciate I could to the reset (which I've done before with some success), but loathed to on a brand new battery.

In all honesty as long as the pack charges fine and performs as expected I would be inclined to keep it and not worry about the 57mAh.
I have 12 packs (8 Tb48's) I had one of them delivered to me with no LEDS upon arrival.
It charged fine and I kept an eye on it for performance for around the first 4 or 5 cycles. It didn't show any signs of lowered performance and took its place in my collection. It is still performing fine.
Obviously your call though.

 

[The Editor]

If my theories about the firmware bug are correct, a new battery that was originally shipped with the buggy firmware from the factory, and which was then stored for several months before it was purchased, could be DOA because of the bug.

Batteries shipped with other versions of firmware, or put into service and updated without long-term storage should be OK.

Just my theory...

Kevin

Yes - this problem only seems to manifest itself for packs that are stored beyond 90days/three months.
None of my packs have gone more than three weeks (and that was due to a holiday) without being used.