Are old battery packs safe?

[E biker]

I read a article that was saying that a battery pack that was loosing its ability to charge all batterys in pack, from use and recharging, over time,can catch fire. The article says the battery maintenance system only works to prevent over charging, but not to monitor the whole battery pack.
It basically says that the pack losing more and more individual cells could lead to a fire.Can this happen? And should I be worried about our batterys being two years old?

 

[E biker]

Thanks for the reply, what may I ask is your expertise with battery life.

 

[m@Robertson]

It basically says that the pack losing more and more individual cells could lead to a fire.Can this happen? And should I be worried about our batterys being two years old?

Cells age over time and lose capacity for sure. But that capacity loss does not create a fire risk. It just creates a battery with less and less range over time. You've heard about the general ballpark life expectancy of 800 cycles for a li-ion (really its a li-nmc) battery? Well that 800 cycle lifespan is usually considered to yield a battery that has lost... 10% of its capacity. In the grand scheme thats not a lot.

Look at it another way: There are companies out there that are using 'worn out' 18650 cells for commercial products. Stuff like home-use power walls. The cells are only down 10%-ish and that means they have been scrapped with 85-90% capacity. There is a whole secondary market building up around batteries that have reached this threshold. If they were inherently dangerous that market would not exist.

There are other things that can cause an old battery to become unsafe, but just the cells wearing down isn't one of them.

If on the other hand the article is saying that there are conditions where an older pack whose cells are out of balance could cause a fire... thats not quite correct, either. First of all, you should balance-charge your pack on occasion. Particularly if you are charging to 80% regularly to preserve pack life. But a pack with a few cells in a group that has gone out of balance is going to under-charge the cell group IIRC, not over-charge it. But a definitive answer on this risk would have to be made with specific knowledge of the BMS involved (meaning you can't be definitive). Best not to let cells get out of balance in the first place, hence the prudent action is to occasionally balance charge the pack.

 

[Jeremy McCreary]

Cells age over time and lose capacity for sure. But that capacity loss does not create a fire risk. It just creates a battery with less and less range over time. You've heard about the general ballpark life expectancy of 800 cycles for a li-ion (really its a li-nmc) battery? Well that 800 cycle lifespan is usually considered to yield a battery that has lost... 10% of its capacity. In the grand scheme thats not a lot.

Look at it another way: There are companies out there that are using 'worn out' 18650 cells for commercial products. Stuff like home-use power walls. The cells are only down 10%-ish and that means they have been scrapped with 85-90% capacity. There is a whole secondary market building up around batteries that have reached this threshold. If they were inherently dangerous that market would not exist.

There are other things that can cause an old battery to become unsafe, but just the cells wearing down isn't one of them.

If on the other hand the article is saying that there are conditions where an older pack whose cells are out of balance could cause a fire... thats not quite correct, either. First of all, you should balance-charge your pack on occasion. Particularly if you are charging to 80% regularly to preserve pack life. But a pack with a few cells in a group that has gone out of balance is going to under-charge the cell group IIRC, not over-charge it. But a definitive answer on this risk would have to be made with specific knowledge of the BMS involved (meaning you can't be definitive). Best not to let cells get out of balance in the first place, hence the prudent action is to occasionally balance charge the pack.

Please tell us how you balance charge a pack. Don't recall the details, but I do recall seeing more than one recommendation on EBR.

 

[PCeBiker]

Please tell us how you balance charge a pack. Don't recall the details, but I do recall seeing more than one recommendation on EBR.

You can leave your battery charging for a Really long time and if that doesn't work, you can buy this stuff and open up your battery to check and charge each cell group.

You don't even need a voltmeter.
There is one built into the power supply.

You only need to know what you're doing.

 

[E biker]

Cells age over time and lose capacity for sure. But that capacity loss does not create a fire risk. It just creates a battery with less and less range over time. You've heard about the general ballpark life expectancy of 800 cycles for a li-ion (really its a li-nmc) battery? Well that 800 cycle lifespan is usually considered to yield a battery that has lost... 10% of its capacity. In the grand scheme thats not a lot.

Look at it another way: There are companies out there that are using 'worn out' 18650 cells for commercial products. Stuff like home-use power walls. The cells are only down 10%-ish and that means they have been scrapped with 85-90% capacity. There is a whole secondary market building up around batteries that have reached this threshold. If they were inherently dangerous that market would not exist.

There are other things that can cause an old battery to become unsafe, but just the cells wearing down isn't one of them.

If on the other hand the article is saying that there are conditions where an older pack whose cells are out of balance could cause a fire... thats not quite correct, either. First of all, you should balance-charge your pack on occasion. Particularly if you are charging to 80% regularly to preserve pack life. But a pack with a few cells in a group that has gone out of balance is going to under-charge the cell group IIRC, not over-charge it. But a definitive answer on this risk would have to be made with specific knowledge of the BMS involved (meaning you can't be definitive). Best not to let cells get out of balance in the first place, hence the prudent action is to occasionally balance charge the pack.

Thanks, I wish I could put a link to the article, but it was saying how dangerous li _on batterys are if some are worn and the pack is old, what is old? It depends on a lot of things I'm shur. Our batterys are 36 volt, and we get 15 miles per charge, less when I pull the dog cart, 20 lb puppy, we don't deplete the pack to empty. I am looking at something with 750 watt motor and a larger battery pack to tote the dog.
We have four battery packs for two bicycles, long story.

 

[6zfshdb]

With age, comes use and perhaps abuse. The older a battery is, the more use it has seen, which may include abuse. Dropping, overheating and other physical damage can definitely lead to a fire. Age alone does not increase the risk.

 

[E biker]

I don't let them set fully charged and definitely not heat or cold, going to go for a Christmas ride later, 50 degrees in northern Indiana! I love it.

 

[Chargeride]

I'd take it to an expert just to take off the cover and make sure all the batteries are still secure, the wiring is unchaffed and there's no possibility of shorts.

 

[m@Robertson]

Please tell us how you balance charge a pack. Don't recall the details, but I do recall seeing more than one recommendation on EBR.

Lets say you ride every day, and you charge every day. Thats 30 charge cycles per month. So at that rate, once a month do a balance charge (which means if you charge less you don't have to do so as frequently). Myself I typically charge twice daily and I still do it just once monthly.

A balance charge is very simply a charge to 100%, but you let it sit at 100% for, say, an additional two to three hours. I hope we all know you should never let a battery pack sit on a charger regardless of whether it is a 'smart' charger or not. And you should also never let the battery sit for any more time than it absolutely must at a 100% charge (this is the part where someone pops off and says their dadburn battery sits for days at 100% and by jiminy it still works after 10 years... which requires the obligatory response of go educate yourself on how li-ion batteries work from an actual knowledgeable source as opposed to listening to some bozo with a keyboard).

Where was I? ... additional hours... right. So why let it sit like that? Because as a battery's BMS senses the pack reaches a roughly 97% or 98% (ish) charge level, it will begin to redirect/apportion current to cells that are a little lower than their neighbors in the cell group, until the individual cells are all 'balanced' at hopefully equal voltage levels.

If you have a current meter on your battery charger, such as what the Satiator has, or one of these with an inline meter, you can tell how long the process takes because you can watch it. The charger will go at full blast (Constant Current mode) from the start until it gets up real close to the target voltage level. Then it will switch to Constant Voltage mode, where the amps being fed in slowly ramp down, until it goes to zero. Usually you think you're done there. Sit and watch it for a bit and it'll start back up again and feed in 0.1a or 0.2a for literally just a second. Then it stops again. This cycle will repeat. What you're seeing is the BMS sharing current to balance the lower voltage cells. The charger sees just enough of a voltage drop to dribble in a little more juice. After awhile this cycle will end and the charger will read done and stay that way. Job done.

 

[m@Robertson]

... and if that doesn't work, you can buy this stuff ...

As of now, two of my three Wanptek power supplies have died on me. The first one died after only a few weeks. The second one took a year or so. Power supplies like these are inviting thanks to their built in display and spiffy dials. But if you want something that lasts the old standby Mean Wells are the way to go.

 

[PCeBiker]

As of now, two of my three Wanptek power supplies have died on me. The first one died after only a few weeks. The second one took a year or so. Power supplies like these are inviting thanks to their built in display and spiffy dials. But if you want something that lasts the old standby Mean Wells are the way to go.

So far so good with my Wamptek power supply. I do all my battery charging with it now and only charge at 2 amps with a maximum of 3 amps.
I'm hoping that will extend its service life and it's better for the battery too.

As long as it doesn't fail in a dangerous way by overcharging or short circuiting my battery.

I'll definitely consider the MeanWell power supply if mine ever fails, but it is nice having the voltage and current display and dials I can turn by hand without needing a screwdriver.

 

[PCeBiker]

A balance charge is very simply a charge to 100%, but you let it sit at 100% for, say, an additional two to three hours.

Someone mentioned plugging your battery charger into a Watt meter to see how much current it's drawing.

I think that's a great idea.

You can check the idle current (or Watts) to see what the charger is using when it's not connected to the battery, then connect the charger to the battery to see how many Watts (or amps) are going into the battery.

When the charger light turns green, the charger has switched to constant voltage.
You know the battery is finished trickle charging when the charger current drops down to the idle current.

That way you know exactly when the battery is done balancing.

Some guys leave the charger plugged in for a few hours and some for a couple days.
The Watt meter removes the guess work.

 

[spokewrench]

This week I had a battery that was down to 48 volts, having run only 8 miles since it was charged 3 months ago. I guess most of the missing power had been vampire power drawn by the bike. When I charged it, I balanced it. The watt meter accumulated 10.5 hours of "on" time before the BMS quit taking any power.

 

[Mily]

If you're worried that your battery is faulty, I guess you could start by measuring its voltage.