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Slightly OT Effective life of the LiFePo4 16850 battery cell

steve-l

Titanium
Joined
Mar 2, 2012
Location
Geilenkirchen, Germany
Perhaps many of you have noticed that this 18650 is the most common Li cell on the market, but there is a myriad of manufacturers, amp hour ratings and prices. It is a mine field. I have spent several hours researching the trade-offs of high capacity verses durability and several things have surfaced.

1) You cannot believe any manufacturer's ratings in either mah or (number)C, because they are often bloated for marketing purposes unless the tests are performed by a 3rd party.
2) No article has directly addressed the question "Is it possible to have both higher capacity without trading off durability (battery cycles)". If yes, how do I discriminate?

Everybody wants lower prices and everybody would enjoy higher energy density, but they are most likely an either/ or issue as opposed to both. I'm looking for some expert knowledge and guidance as to how to select the best cell. All of my battery packs will include a battery manager. I have invested in a battery strip spot welding machine to rebuild or manufacture my own battery packs
 
You are beating a dead horse with LiFePo4 16850's

Hardly anybody manufactures 18650 size in LiFePo4 chemistry and most of the manufacturers are questionable chinese brands.

If you intented to talk about (other) Li-ion abtteries (not LiFePo4) for power tools the Sony VTC4, VTC5 and VTC6 are exellent choices. Sony VTC's are Lithium nickel manganese cobalt oxide (LiNiMnCoO
2 or NMC chemistry.

Problem is that buying genuine ones is tricky at best. Your cheapest reliable source for genuine Sony cells is probably...guess what.. Makita battery packs during promotions!
 
You are beating a dead horse with LiFePo4 16850's

Hardly anybody manufactures 18650 size in LiFePo4 chemistry and most of the manufacturers are questionable chinese brands.

If you intented to talk about (other) Li-ion abtteries (not LiFePo4) for power tools the Sony VTC4, VTC5 and VTC6 are exellent choices. Sony VTC's are Lithium nickel manganese cobalt oxide (LiNiMnCoO
2 or NMC chemistry.

Problem is that buying genuine ones is tricky at best. Your cheapest reliable source for genuine Sony cells is probably...guess what.. Makita battery packs during promotions!

I think you missed the mark a bit. First the 18650 format is probably the most common form being manufactured today........still. It is being used in virtually all electric car batteries. Second, the LiFePo4 chemistry is still the safest chemistry in use. It is also possible that the 18650 form will out survive the chemistry when it is eventually superseded. At the moment, I don't have an interest in any other format, just the 18650. You have also not answered my query, how do I discriminate between cells that advertise 15000 mah and others that advertise only 3000 mah? What are the trade-offs?
 
I think you missed the mark a bit. First the 18650 format is probably the most common form being manufactured today........still. It is being used in virtually all electric car batteries. Second, the LiFePo4 chemistry is still the safest chemistry in use. It is also possible that the 18650 form will out survive the chemistry when it is eventually superseded. At the moment, I don't have an interest in any other format, just the 18650. You have also not answered my query, how do I discriminate between cells that advertise 15000 mah and others that advertise only 3000 mah? What are the trade-offs?
Fair enough, you want LiFePo4 for safety.

18650 is very common BUT not in LiFePo4 chemistry. Not too many manufacturers, all chinese made, sold with various rebranded names.

Anything much over 1800 mAh from 18650 LiFePo4 chemistry is impossible so rule out everything advertised as over 1800mAh or so.

Trade-off between high capacity and low capacity is usually allowed discharge current. (you can also find low current, low capacity cells if you want to.)
Selection is pretty sparse on Lifepo4 but this gives you pretty good idea NKON | Rechargeable batteries - 18650 : LIFEPO4
1800mAh 5.4A max current
1100mAh 33A max current

As to what you actually get and how is cycle life... absolutely no fucking idea unless you are size of VW or Tesla company.
Did I mention that most of LiFePo4's are rebranded and all of them are chinese made in unknown factory with unknown specifications?
What you get tomorrow can be totally different battery from yesterday unless you have few million budget &QC to deal with the chinese factories directly.

edit: above linked nkon.nl webshop has good reputation and the cells sold are Enerpower branded ones. Enerpower is probably one of the more reliable suppliers and you can even find some sort of specifications for the cells
LiFePo4 Batteries – ENERpower

Good news: only the 1100mAh model has enough high discharge current for hand tools so it leaves you grand total of one (1) 18650 size cell suitable for hand tools. No need to fuss about too much selection :D

Not too many suppliers either that I'd trust: nkon.nl, enerprof.de and akkula.fi
 
Mattij,
Thanks for the education. It allowed me to go to more places and search out the answers I wanted. I found the battery I needed, I would attach the spec PDF, but I don't think I can. It only has a 1200 mAh rating. It is a Valence cell APR18650M1B, by LithiumWerks.
 
Mattij,
Thanks for the education. It allowed me to go to more places and search out the answers I wanted. I found the battery I needed, I would attach the spec PDF, but I don't think I can. It only has a 1200 mAh rating. It is a Valence cell APR18650M1B, by LithiumWerks.

Should be a decent choice if its anything like original A123 systems cell.

I have some old stock APR18650M1B from A123 systems before it went bankrupt 7? years ago or so.
A123 Systems batteries would have been my recommendation but availability has been kinda shady for long time. LithiumWerks looks like legit follower for A123 Systems nanotechnology.

A123 Systems had factory in US and they were having some problems with large format cells (Fisker Karma automotive battery fiasco)
Apparently the smaller 18650 format cells from their chinese factory were never a problem.
 
There are multiple reputable manufacturers of 18650 cells, in various chemistries and optimizations, for industrial, medical, military, etc. markets, You just need to talk to a battery pack integrator company. They should be able to get you loose cells suited for your specific application (and, if you need, weld them into packs, add safety and/or charging controls, lead wires, connectors etc.).

OTOH E-bay, hobby sites, etc. on the web may not be your best source for cells of good pedigree & realistic specifications.
 
What are the packs going to be for? Voltage, capacity, amp draw? Lots of different things to consider, but generally higher (genuine) capacity = quicker capacity loss under the same conditions. No free lunch there unfortunately. Another good source of battery tests and info is Endless Sphere, an ebike forum. I learnt a lot about different chemistries, tab welders and so on. When I rebuild my current bike battery (2nd at 22000 miles :( ) I definitely won't be using Sanyo ga cells as they suck balls for longevity.
 
What are the packs going to be for? Voltage, capacity, amp draw? Lots of different things to consider, but generally higher (genuine) capacity = quicker capacity loss under the same conditions. No free lunch there unfortunately. Another good source of battery tests and info is Endless Sphere, an ebike forum. I learnt a lot about different chemistries, tab welders and so on. When I rebuild my current bike battery (2nd at 22000 miles :( ) I definitely won't be using Sanyo ga cells as they suck balls for longevity.

The reason for my effort is that I own a Segway X2 Golf model that I bought myself on my retirement in 2011. I have been very careful from new with the X2's use and storage environment. It has always been stored in a heated space. I now have 9 years of significant annual use and the batteries are as good now as they were new as far as charging time and range, but I think I'm on borrowed time for the batteries, as 5 years is considered very good longevity. New batteries cost $1800 from Segway. Here is the rub. Segway is no longer an American company. It has been sold to a Chinese group. Segway has virtually abandoned the original products and the old support structure and those dealers. The company is now selling cheap crap scooters.I have no confidence that their replacement batteries are of the same quality they used to be. They are being made in China. I think the risk of fire is very real if the wrong chemistry or poor quality cells are used. Based on my perceived risk, I have decided to build my own. The cost of new batteries leaves economic room to tool up to make my own replacements and thereby control the quality. The X2 is just too expensive to risk a destructive fire.
 
A good source of very high quality 18650 cells is DeWalt or Milwaukee (or whoever) cordless drill batteries. They are a little expensive when sourced that way but they are very well matched with decent capacity and high output current. I've made some good sized packs with them and they work awesome. I use a Hyperion balancing charger and run discharge/charge cycles on the individual cells before making packs so that the individual cells can be matched for capacity and internal resistance.

The cheap Chinese cells with ridiculous capacity claims are absolute garbage, stay well away from those. I got one with a laser pointer that was marked "4800 mAH" - so I tested it with my charger cycle. I shit you not, actual capacity was 158 mAH.
 
A good source of very high quality 18650 cells is DeWalt or Milwaukee (or whoever) cordless drill batteries. They are a little expensive when sourced that way but they are very well matched with decent capacity and high output current. I've made some good sized packs with them and they work awesome. I use a Hyperion balancing charger and run discharge/charge cycles on the individual cells before making packs so that the individual cells can be matched for capacity and internal resistance.

The cheap Chinese cells with ridiculous capacity claims are absolute garbage, stay well away from those. I got one with a laser pointer that was marked "4800 mAH" - so I tested it with my charger cycle. I shit you not, actual capacity was 158 mAH.

Thank you for that input. Your experience exactly matches my fear. I am now searching for a supplier of pure nickel sheet to establish the required voltage planes via spot welding as opposed to using nickel banding. The Segway battery uses multiple blocks of cells in individual groups. These blocks have cells spot welded together on common nickel sheets. According to the BMS specs. the max current will not exceed 20 amps, so I think the minimum sheet thickness should be .02 mm. Please correct me if I am wrong. The only supplier I have found offers this sheet in hard or half hard. I would prefer annealed, but I can't find it.
 
funnily enough Steve I have a friend who has a Segway with dead batteries (didn't leave them on the charger). I looked into replacement cells for him and even at $4 a cell it came out to $400 or more, can't remember exactly. I think his packs were 11S5P or there abouts and there were 2 of them. I had no idea whether or not the battery protection boards would still work having been unpowered for so long and my friend didn't want to gamble $400 on finding out, so nothing ever came of it.

For connections, you can use 0.1mm x10mm nickel strip for series connections and sandwich 0.1mm copper sheet under it for parallel connections. Works very well. I bought the cells for my bike battery (sadly screwed up the BMS in the process) from a guy in Europe for very reasonable money - $155 for 45 new but spot welded Sanyo GA cells. Top of the line cells that are $10+ each. They all checked out as 100% legit. At the time he had some 18650 lifepo4 cells for reasonable money. PM and I can send you a way to contact him.
 
funnily enough Steve I have a friend who has a Segway with dead batteries (didn't leave them on the charger). I looked into replacement cells for him and even at $4 a cell it came out to $400 or more, can't remember exactly. I think his packs were 11S5P or there abouts and there were 2 of them. I had no idea whether or not the battery protection boards would still work having been unpowered for so long and my friend didn't want to gamble $400 on finding out, so nothing ever came of it.

For connections, you can use 0.1mm x10mm nickel strip for series connections and sandwich 0.1mm copper sheet under it for parallel connections. Works very well. I bought the cells for my bike battery (sadly screwed up the BMS in the process) from a guy in Europe for very reasonable money - $155 for 45 new but spot welded Sanyo GA cells. Top of the line cells that are $10+ each. They all checked out as 100% legit. At the time he had some 18650 lifepo4 cells for reasonable money. PM and I can send you a way to contact him.

There are 92 cells in each battery pack and 2 battery packs are required. I will buy 200 cells and at that volume, I expect to see my cost below $2.50 a cell. I have found a source of .2mm pure nickel sheet to construct the voltage and ground planes. Max expected current is 20 amps and ,2mm should be OK for that. I have also found replacement BMS boards at a reasonable price. So the initial cost of replacements could be equal to or slightly greater than the cost of a new battery purchase, but any more builds beyond the first pair will be less money. However, pure nickel is spendy at almost $13,000 a ton. A single sheet of .2mm thick foil 30cm wide and a meter long cost me $150.

On another note, leaving the batteries on a charger, even with the best BMS firmware is a bad idea. Correct is a bump charge every 2 weeks for just a few minutes keeping the charge at around 80% at room temperature is the hot setup for storage and longevity.
 
On another note, leaving the batteries on a charger, even with the best BMS firmware is a bad idea. Correct is a bump charge every 2 weeks for just a few minutes keeping the charge at around 80% at room temperature is the hot setup for storage and longevity.

No reason to bump charge every 2 weeks, even once per year is sufficient. Li battery at 80 % SOC discharges to maybe 75 or 70% SOC in in a year.
 
No reason to bump charge every 2 weeks, even once per year is sufficient. Li battery at 80 % SOC discharges to maybe 75 or 70% SOC in in a year.

Maybe so, but a two week bump charge has allowed a 9 year life span and still going......jus sayin! I think the real key in temperature control for Li batteries. They seem to fail quickly if left exposed to either high or low temperatures.
 
Actually cold storage (just NOT below freezing) is supposed to increase their life considerably from what I've read. I have a set of little drone batteries I bought a bulk pile of (small Li-Po batteries) that I bump charge about once a year. I keep them in the fridge in a sealed plastic baggie in the meantime. They usually don't need much of a charge at all. I bump them to 60% S.O.C. and they hang right there, very slight drop over a year.

There was a white paper about this I read that circulated at an electronics forum I am a member of - must have been near 5 years ago - I think from a German university professor. Lower to mid state of charge and low temperature for longer term storage was confirmed as optimal in his study as I recall.

Edit: if you haven't run across Battery University before now, you should check it out. Pretty good info there usually. Just found this link there regarding lithium battery lifetime expectations and ways to increase them:

How to Prolong Lithium-based Batteries - Battery University
 








 
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