Technical Corner: Battery Pack Safety and "Best Practices"

CloneWerks

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Coming into this group from the perspective of an EV car owner and a long time R/C enthusiast I have an extensive background with the care and feeding of various battery systems, especially Lithium Ion (Li-ion) packs.

NOTE: Portions written in italics represent my personal opinion/feelings/observations and should be taken with due consideration.

I mention this again later in the article, but this part is important! ANY PACK THAT IS DEFORMING OR BULGING NEEDS TO BE TAKEN OUTSIDE TO A SAFE, NON-FLAMABLE, LOCATION IMMEDIATELY!

Okay so let's move on;

The first and most basic thing to understand is that there are two basic types of battery packs.

"Unprotected" where the internal cells are just attached in an electrical circuit and there is no form of monitoring or regulation. This style includes most R/C car types, cell phone batteries (the electronics in the phone itself handles the monitoring) and some laptop batteries (also regulated by the laptop itself).

"Protected" where the pack itself has a BMS or Battery Monitoring System inside that controls what happens with the battery and protects it from;
  • Over-Current
  • Over-Charge
  • Over-Discharge
  • Short Circuits
In most eBike battery packs I've see the BMS is also a Balance Charge Monitor because the actual charger that you plug into the wall is usually pretty "stupid" and just provides power.

Any -quality- battery pack should be of the "Protected" type. If a battery pack has one (or more) of the following certifications you can be reasonably confident that it has a robust BMS circuit built in; EN15194:2017, UN38.3, UN-package, UL, CE, FCC, CB, ROHS.

However, problems can still crop up, possibly due to things like a factory defect, or long term damage from the vibrations and/or physical impacts that a bike is constantly subject to during use. It is therefore a wise choice to follow some common guidelines (hereafter referred to as "best practice") to prevent issues.

1) ONLY charge your battery pack in a fireproof location.
I absolutely WILL NOT charge my battery packs "on-bike". I personally recommend that you NEVER charge your packs inside the main living area of your house. In my case both battery and charger go into a large-ish metal toolbox that sits on a ceramic tile (from home depot flooring) outside in my screened-in back porch. I leave the toolbox open so that the charger gets plenty of air circulation. Listen to me, Li-ion fires are no joke [link], you must show a battery pack due respect!

2) Prevent overcharging
The BMS should prevent this from ever happening but why take a chance? Get an inexpensive wall timer and set it to limit charging time. I use this one and set it for about 5 hours, but if you do a search on "plug in countdown timer switch" in amazon you'll get a bazillion options.

3) Prevent over-discharge
Again the BMS should prevent this from ever happening by cutting off your battery power while the pack still has a safe internal charge, but why risk it? If you get down to the last bar on your indicator then stop and charge your battery as soon as you can. Yes I understand you could easily wind up on a long ride with no choice, if so then do what you have to do, just don't make it a regular practice to run so low.

4) Store with a proper charge level
If a Li-ion pack is going to sit idle for an extended period (say more than a week) then it should be charged or discharged until it's at roughly 50%. This will give you a far better battery life than leaving it fully charged and leaving it at a very low charge -will- degrade the battery fairly quickly. If you are leaving it idle for an even longer time, say for the winter months, you should check the charge every month to make sure it's still around 50% as Li-ion batteries self-discharge over time.

5) Inspect the pack regularly for damage or bulging
The pack on an eBike lives a somewhat rugged life and is subject to constant temperature changes, bumping, vibrations, and physical shocks. This makes it very important that you inspect the pack regularly (in my case every time I remove or install it). Check the connectors for any damage, discoloration, or signs that something might have overheated/melted. Check around the connectors for any stress cracks or anything that looks unusual. The same with the body of the pack. MOST IMPORTANTLY watch for ANY signs that the pack is deforming or bulging. ANY PACK THAT IS DEFORMING OR BULGING NEEDS TO BE TAKEN OUTSIDE TO A SAFE, NON-FLAMABLE, LOCATION IMMEDIATELY! If you don't know how to decommission a damaged battery pack (let's be honest, nobody but a professional really does) contact your local fire department (non-emergency number please) and explain the situation and they will assist.

Following these basic guidelines should give your battery pack a long and happy service life and prevent any tragedies from occuring.

EDIT: Adding a new video link to a good battery maintenance overview.
 

JerryB

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Seems like some well thought out advice. Question.....why do none of the ebike companies make these same points? Don't they have some liability in the game?? Like almost anything....understanding a product is important....can an ebike battery explode or cause a fire....yes.....but so can my propane grill if not used properly. Be aware...be smart....enjoy your ebike and a good steak.
 

CloneWerks

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Seems like some well thought out advice. Question.....why do none of the ebike companies make these same points? Don't they have some liability in the game?? Like almost anything....understanding a product is important....can an ebike battery explode or cause a fire....yes.....but so can my propane grill if not used properly. Be aware...be smart....enjoy your ebike and a good steak.
To be perfectly blunt, it costs them money to take on the liability, write manuals, do warnings. Here in the United States it's worth all that effort because we are so lawsuit-happy but many other places (I'm looking at you China) don't bother with any of it until bad things actually happen and then they play "catch up". You see this a lot in the R/C hobby arena and you also see it a lot in my other favorite thing, high power/high end flashlights (most of which are powered by the exact same 18650 cells that make up a bike battery). You would freak if you saw some of the janky s**t that used to be sold before some standards were put in place and there are still a lot of China/Taiwan/India produced crap 18650's out there that are just sticks of dynamite waiting to go off.
 

Snoop

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This is the label on my Aventon’s battery.

3E902E7F-1B0D-48AC-A9BC-91AC5A730682.jpeg


Should I consider it “Protected”?
Did a Google search on the model number and came up blank, and their website is non-informative on the matter.
 

CloneWerks

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Are there any stickers on it (UL - underwriters laboratory) or CE mark?
is it the one that looks like this?

2022-09-04 15_07_18-Aventon Battery - Opera.jpg
 

Snoop

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The charger has a UL mark on it, though.

Does that count?

FE322395-D33A-45A0-970D-FF3053A65BC4.jpeg
 

CloneWerks

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Darn, because the one I showed is a variant production model of the L460 Reention Dorado which I have discovered is a -really good- battery pack.

So it's good that your charger has UL and CE certification. That raises the quality level considerably but still doesn't tell us anything about the battery pack. Given the way eBikes work it pretty much -has- to have a BMC (i.e. be protected) but as to the quality of the BMC board... anyone's guess at this point though Aventon does have a reputation to protect.
 

Snoop

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Darn, because the one I showed is a variant production model of the L460 Reention Dorado which I have discovered is a -really good- battery pack.

So it's good that your charger has UL and CE certification. That raises the quality level considerably but still doesn't tell us anything about the battery pack. Given the way eBikes work it pretty much -has- to have a BMC (i.e. be protected) but as to the quality of the BMC board... anyone's guess at this point though Aventon does have a reputation to protect.

Thx!
 

drofgnal

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I've pretty much settled on the fact that my bike will be a bosch mid drive system. Their chargers are certified to UL 1012, and the entire ebike system (battery, charger, drive system and display) are certified to UL 2849. It is important to make sure the entire system is UL certified. I asked another bike manufacturer if they were UL certified and they said they are working on it and plan to have that in place in the future. They were marked off my list.

I have some ekxperience through work with LI ion 18650 cells. The cell itself has built in protection.

Short circuit protection
protection circuit in the anode protecting against overcharge, over discharge, short circuit and overheating
pressure relief valve in the event gasses build up and need relief. (sort of a last protection)

The battery built up of an array of 18650 cells will have it's own protection for external cell to cell and cell to case short circuit protection, usually by physical and mechanical design of the battery preventing short circuit. A key factor is what environmental stresses (loads, vibration, shock etc) the battery is designed to take and still maintain short circuit protection. It's important to not knock them around more than the design allows. The case should be very robust. If for some reason the case becomes compromised the battery should be recycled even if usable.

The charger also has it's own protection circuits to prevent charging over voltage protection, charging over current protection, charging/discharging over temperature protection, reverse polarity protection, short circuit protection, and over voltage and deep discharge protection (getting below 20% charge). Finally some of this same protection needs to be in the drive electronics as well, hence the overall ebike UL certification.

Even with all these protections a failure can occur and I know of one (not an ebike application). I'd guess it was due to physical stress on the battery causing internal cell to cel; short, but I don't know for sure. The system overheated and failed. But other protection measures would have kicked in to prevent fire or explosion, just the system was then unusable.

I never thought about it much until I started researching ebikes. I have several 18v Li ion power tool batteries in the garage where they've always been stored regardless of the temperature extreme cold or hot. I had one battery over the years fail, just wouldn't charge or discharge. I assume a protection mechanism kicked in and I dropped it off at batteries plus for recycling. I have one 40 watt leaf blower with Li ion battery as well. Garage stored. I'll probably get some protective storage bags for these batteries after having done some research.

So after some research any ebike i get will have the battery charger certified to UL 1012 and the entire ebike system certified to UL 2849. So far the only one I know of is a Bosch system.
 
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