Mixing old and new LifeP04 batteries

[miataroadster]

I just bought two 200w solar panels plus needed parts to complete the installation. This addition will give me a total of 600w (more like maybe 400w realistically?). I have two 100ah LiFePO4 batteries in parallel.

I am thinking of buying one or two more of the same batteries, but I noticed the website says batteries MUST be purchased within a month! Is that just a sales pitch? Hmmm..the current pair I have was bought 13 months ago.

What is your experience in mixing old and new batteries. All will be same brand, size and ah.

 

[PhilFromMaine]

I just bought two 200w solar panels plus needed parts to complete the installation. This addition will give me a total of 600w (more like maybe 400w realistically?). I have two 100ah LiFePO4 batteries in parallel.

I am thinking of buying one or two more of the same batteries, but I noticed the website says batteries MUST be purchased within a month! Is that just a sales pitch? Hmmm..the current pair I have was bought 13 months ago.

What is your experience in mixing old and new batteries. All will be same brand, size and ah.

That "MUST" is just a sales pitch. They should have said "IDEALLY". People mix and match all the time now. For a novice, you need to do your due diligence on the procedures that you need to follow to get the best matching.

Years ago, when 12v lifepo4 batteries first became widely available, people in the field didn't recommend combining differing aged batteries, but with time that has been disproven. Study up on the best practices for combining different aged batteries.

 

[Aussieguy]

X2 what Phil saided

 

[jlankford]

Study up on the best practices for combining different aged batteries.

Do you have a link for that, or a hint on where to search? My searching yields that in general yes, this is OK... what are the "best practices" you have in mind?

 

[Aussieguy]

solar forums are good info...

they even swap out lead acid within a big bank

https://diysolarforum.com/threads/c...specifically-fortress-eflex-or-similar.37241/

Google https://www.google.com/search?client=firefox-b-1-d&q=combining++lifepo4+batteries+of+different+ages

...

 

[jlankford]

solar forums are good info...

they even swap out lead acid within a big bank

https://diysolarforum.com/threads/c...specifically-fortress-eflex-or-similar.37241/

Google https://www.google.com/search?client=firefox-b-1-d&q=combining++lifepo4+batteries+of+different+ages

...

I saw that thread. That's mostly where I did my searching. But I don't see any specific details there about what to do for a "best practice." Just a lot of analysis details that boil down to it's OK to do this with different age batteries in parallel. Using the same capacity size, brand, etc, but that's true even when combining new.

 

[Aussieguy]

I have 200ah battery + 740w solar
12v fridge ... and use all my 12v stuff including furnace
50 amp MPPT

works great .... as long as you don't want to run a lot of Inverter power

my batteries are topped up by 2 pm most days
will last about 3 days if no sun... solar is NEVER switched off unless servicing


get a decent MPPT before you look at more battery
even on bad days solar will probably stop any further discharge during the day

put all your stuff together and try it .... you might be pleasantly surprised

camping spots.... look for semi shaded spots where you get shade in the afternoon

 

[MR.M]

IMO if you want the barrtries to be able to balance with each other like they need to do with lithium then having batteries that are the same age will make a difference . a yr old lithium can have issues with a brand new one when hooked up in parallel . but don't take the manufactures word or mine for it . test it yourself and then let us know how it goes .

 

[ppine]

Two 100aH Li batteries will suffice for 600w solar panels.
Charge the batteries and then hook them together in parallel with no load on them for a day. Then they are ready to go.

 

[TacomaJoe]

I agree with the "go ahead and parallel" crowd. I started with a DIY 280Ah battery then added two DIY 277Ah batteries a year later. A year after that I bought the then cheapest 100Ah battery on Amazon and threw it into the mix with no problems. I know what's going on with my DIY batteries because of the smart bluetooth BMS.

The caveat in OPs case is LiTime batteries. There have been issues with the BMS in them going to standby/sleep at the top of the charge cycle and then not waking up because the other battery in the parallel group woke up and took the load. The BMS operations would need to be verified in this case.

 

[TitanMike]

I think the real answer will depend on the batteries themselves. The manufacturers may have a variety of answers depending on who's providing it. Is it someone in marketing or from their engineering department.

Some mfr's may know of an internal issue exacerbated by age difference and state a very short age difference. I wonder how much age difference exists in their warehouse inventory of same model/size batteries considering how it might take up to 60+ days for sea transport from China. Chance for mismatch is great as old and new meet in the warehouse.

At the other end of the spectrum Battleborn states age difference between their batteries in parallel can be up to two years.

What may apply to one battery. Will not necessarily apply to others. Especially when considering there are three different cell types represented in lifepo4 batteries (cylindrical, prismatic, and pouch) along with a plethora of BMS mfrs.

 

[PhilFromMaine]

Do you have a link for that, or a hint on where to search? My searching yields that in general yes, this is OK... what are the "best practices" you have in mind?

The original post is a simple question from a novice (which we all were at one time). For that question I was only thinking of balancing the batteries and the type of parallel configuration used as best practices. The original poster is talking about 2 batteries which is as simple as can be.

I did check my folders and resurrected this 2 year old Will Prowse video where he wires up numerous lifepo4 batteries of different size, brand, and capacity. It is way overkill for this thread, but covers all the basics and much more. Note Prowse recomends using buss bars with equal lengths of wire to the batteries when using numerous batteries in parallel.

 

[Aussieguy]

and Andy at the Off grid garage (Youtube)
he connected multiple different sized batteries (Capacity) together

cant remember which ANDY or Will , had a very good explanation about battery internal resistance voltage and SOC .
but in laymans terms... get the batteries or cells to the same voltage before connecting ... this avoids any large amp draw between battery/cells

test your connections.... any hot ones (finger touch) look to make sure clean and tight or a bad crimp

research and decide for yourself/

https://www.google.com/search?clien...ct+different+sized+lifepo4+batteries+together

Frankenstein 48v built from cells of different ages/sizes
he still uses it for experiments etc 18 months later
https://www.google.com/search?client=firefox-b-1-d&q=off+grid+garage++frankenstein

 

[miataroadster]

I agree with the "go ahead and parallel" crowd. I started with a DIY 280Ah battery then added two DIY 277Ah batteries a year later. A year after that I bought the then cheapest 100Ah battery on Amazon and threw it into the mix with no problems. I know what's going on with my DIY batteries because of the smart bluetooth BMS.

The caveat in OPs case is LiTime batteries. There have been issues with the BMS in them going to standby/sleep at the top of the charge cycle and then not waking up because the other battery in the parallel group woke up and took the load. The BMS operations would need to be verified in this case.

I was not aware of BMS issues with LiTime. So far, my batteries are not giving me issues. We'll, at least if one day it happens then I could check it.

 

[miataroadster]

IMO if you want the barrtries to be able to balance with each other like they need to do with lithiu m then having batteries that are the same age will make a difference . a yr old lithium can have issues with a brand new one when hooked up in parallel . but don't take the manufactures word or mine for it . test it yourself and then let us know how it goes .

Hahaha. It would be an expensive experiment! But if the battery price goes even lower
, I might just do it.

 

[TitanMike]

I was not aware of BMS issues with LiTime. So far, my batteries are not giving me issues. We'll, at least if one day it happens then I could check it.

LiTime BMS issues are not certain for all their batteries. Just the fact they seemingly occur more frequently than with other batteries.

Could be because they're trying to build a product as inexpensive as they can and have also designed their BMS to do things others don't seem co consider all that necessary. That or the other's BMS does it better without issues.

Apparently they know their faults and only warrant their batteries with >30 amp hour capacity for 5 years. Half that of others.