LiFePo4 Battery & Replaceable BMS

[INTJohn]

Manjufacturers market these batteries as having a 3000 to 5000 cycle life and or a 10 year lifespan. The strength of these types of batteries - the BMS (Battery Management System) - is also their weakness. Also, while the battery itself is marketed as lasting over 10 years, they generally carry only a 5 year warranty. Why is this?

If the BMS might fail after 5 years, then why don't manufacturers make these 10+ Year batteries with a Replaceable BMS? instead of consumers being stuck with a 500$ to 1000$ paper weight?

Obviously, those who build their own battery system, wiring cels & BMS accordingly have this option and are capable of this replacement ability but what about the average consumer who purchase these batteries with a completely encased BMS only to have it fail turning the battery into a 30 pound paperweight, even tho the battery itself is still very functional if only said BMS unit could be replaced?

Discuss.........
Thanx,
INTJohn

 

[tx2sturgis]

A few weeks back, maybe a month ago, I was looking over a battery website and it indicated the case can be opened and the BMS was replaceable...trouble is I can't remember what brand of LifePo4 batteries I was looking at....it's been awhile.

If I run across that website again I'll post the link.

 

[bullfrog !]

I think Wil Prowse has done a review on one you can open up.

 

[RvNaut]

still very functional if only said BMS unit could be replaced?

The cells in the battery, are just cells... most like I or others would buy to build their own. If a battery costs $600, $500 is the cells and $100 is the BMS. IOW .. BMS are inexpensive. So when/if the bms dies, take it apart , buy a BMS and build a new battery. It isn't that hard. Project boxes are readily available.

 

[jonyjoe303]

I build my own lifepo4, as long as you can open up the case and get to the wires, replacing the BMS isnt too much of a problem. The cells will last for 10 years easily if they arent cycled everyday.
The 220ah lifepo4 I built is going on 5 years being used 24/7 it still has the original BMS. Failure of a BMS would probably be rare. I never had one go bad.

The only hard part would be wiring the BMS properly, Also get a quality BMS that can handle the amps you need.
The endless sphere forum is where I go when I need info on batteries/BMS.

One thing I did noticed on some BMS, if you drain the battery to where it activates, sometimes the BMS will reactivate and continue to work but if drained again it will reactivate but then stop working. I think some BMS can only be activated several times and then a failsafe prevent them from working again. Replacing the BMS was the only option for me.

This happened to me on the enovate medical battery packs (li-ion 26ah each) I have 12 of these connected in parallel for 312ah battery bank. I had to replace the BMS on 8 of them after I drained them to low. With the new BMS they are working like new again. This batterybank has been running for 3 years 24/7 , I use them to power my fridge. I only charge these to 12.4 volts and charge them once a day, before I would charge them once a week and sometimes the voltage would get too low. This would be like the situation you describe with the BMS no longer working but cells still good. These packs have 4 screws to remove and the wires were easy to get to.

 

[rruff]

Manjufacturers market these batteries as having a 3000 to 5000 cycle life and or a 10 year lifespan. The strength of these types of batteries - the BMS (Battery Management System) - is also their weakness. Also, while the battery itself is marketed as lasting over 10 years, they generally carry only a 5 year warranty. Why is this?

In fact your real warranty lasts as long as Amazon covers it... 30 days typically... or longer if you buy in Nov and they extend it to the end of Jan for the holidays. IME (with Powerqueen).... if you try to collect on a warranty, they will give you endless run-around... seriously, you'll spend many hours doing tests and taking videos to show them what's wrong, and then they will make up bogus stories about how "it's really fine" assuming you are an idiot. And this was when I still had the Amazon warranty!

The problem I had was that the BMS wasn't working properly. It would cut out when the battery got to 13.9V. In their own manual they recommend charging up to 14.6V using a charge controller, which means the BMS should cut out at a higher voltage... as you never want your BMS to be the thing that limits the charge. Typically the BMS will cut out at 15.0V if all the cells are balanced (3.75V per cell), but they actually trip if any cell exceeds 3.75V. At first I thought it was just out of balance for some reason, so I repeatedly charged it at a very low rate so the BMS could do its thing... but it never did. It actually got a little worse.

Anyway, I'd assume that if you have an issue 1,2,3 years down the road, they will claim it's fine, unless it's completely dead... in which case they will claim you did something wrong. In the off chance that they feel generous, you will get prorated from MSRP, and will have to pay shipping both ways, and it will cost about as much as just buying a new one.

BTW... I'm 99% sure they took my defective battery, and... sold it to someone else. Hardly anyone tests these things, and it did "work".

 

[rruff]

Another thing, John... I don't believe the BMS is the weakness, as it's a solid state device and should just work, unless it's defective at the beginning. The battery cells are the weak link. And if you are buying a $200 1280Wh battery, I wouldn't expect much from it in any sense.

In my case I suspect that a bad cell was the real culprit, and the voltage was so far out the BMS couldn't cope with it. Or maybe the BMS was never properly set... it was a newish model, the trolling version, which had low temp cutoff as well as a higher powered BMS.

I recall you saying you have a LiTime and theirs come from the same factory as Powerqueen.

I have a GoKwh battery now that was given to me by the company, and it's performing as it should. It also has scews in the lid and can be taken apart without destroying it.

If I was to buy one, I'd look for one with a low temp cutoff as well as BT in the BMS, as these are not very expensive upgrades now. The BT will let you see what is going on with the individual cells.

 

[INTJohn]

After reading the info & responses & the more I think about this stuff, replaceable BMS for these batteries is prolly a matter of cost effective efficiency by manufacturers.

The odds of a BMS malfunctioning being so low that its simply not worth bothering with the cost of designing & implementing within the manufacturing process a replaceable system. Also, the cost to the consumer of purchasing LFP4 batteries has dropped tremendously just over the last 2 years alone. 100Ah batteries can be bought today for 200$, some even less tho I wonder about quality in such a "bargain battery". But neither will I pay 500$ for even a "solid quality" LFP4 battery. As the price has come down so to, I guess, is the concern for malfunction as if one only gets 4 years out of the thing its still only 50$/yr. Why bother?

Of course, a few years back, it was far more economical, IF one had the ability & time to simply make their own to do so; one then had the option of a replaceable BMS if a glitch occured but today with plummeting prices for LFP batteries I don't even see DIY as a viable economical option unless one simply enjoys the idea of "Building my Own" or if one desires a high Ah battery system, I can see where DIY may still be a viable economical option.

But for a typical vehicle dweller, such as myself, 200ah of battery is plenty - 400$ to 500$ and this can be accomplished with 2 100 AH LFP4's or even 1 200Ah, tho I prefer to not put all Ah's into 1 battery; think "eggs-basket" here.

INTJohn