Hi.

I asked this question on an AI website, https://platform.openai.com/playground and this was the reply. Do you agree?

Can I mix batteries with the same amp hour rating but different brands? Yes, you can mix batteries with the same amp hour rating but from different brands. However, it is important to note that the batteries should be of the same type (i.e. lead acid, lithium-ion, etc.) and that they should be charged and discharged at the same rate to ensure proper performance.

In the case of LIFEPO4, you can mix different brands and capacities as long as each batterie has their own BMS and all batteries are connected to a common bus bar. 

Edited February 9, 20233 yr by zivva

Also check the number of cells per battery. Not a good idea to mix 15 and 16 cell batteries.

13 minutes ago, zivva said:

as long as each batterie has their own BMS and all batteries are connected to a common bus bar. 

Does this also apply to say SunSynk batteries, where the latest ones are manufactured by BYD and the previous ones by CATL - SunSynk says that they're not compatible with each other.

And then to follow up, can one then add a 5Kwh battery to an existing 10Kwh battery by the same manufacturer, provided they have their own BMS?

25 minutes ago, zivva said:

In the case of LIFEPO4, you can mix different brands and capacities as long as each batterie has their own BMS and all batteries are connected to a common bus bar. 

I forgot to mention: The question is with regards to lead-acid batteries. It has the same 180AH rating, both 12V & both lead-acid. Can I use them together in series?

17 minutes ago, Kalahari Cruiser said:

Does this also apply to say SunSynk batteries, where the latest ones are manufactured by BYD and the previous ones by CATL - SunSynk says that they're not compatible with each other.

And then to follow up, can one then add a 5Kwh battery to an existing 10Kwh battery by the same manufacturer, provided they have their own BMS?

BMS might be different between the SunSynk BYD & CATL, so you can not connect their BMS together or can not get communication between the inverter, BYD & CATL.

If different model / brand / capacity you may have to rely on proper inverter voltage settings & BMS of each pack as a last ressort to avoid over / under charge or discharge.

As long as your voltage settings are correct on the inverter side, communication between the inverter & batteries BMS doesn't matter, so you can mix models / brand or capacity 

I would not connect a battery to an installation if the supplier does not specifically indicate that the battery and comms are compatible with the existing installation. Charging and discharging lithium cells blindly is a recipe for disaster.  

3 hours ago, frivan said:

I would not connect a battery to an installation if the supplier does not specifically indicate that the battery and comms are compatible with the existing installation. Charging and discharging lithium cells blindly is a recipe for disaster.  

BMS protect the batteries. Communication between the battery BMS and inverter is totally optional : communication or not, BMS stops charge or discharge if out of specs ...

1 hour ago, zivva said:

BMS protect the batteries. Communication between the battery BMS and inverter is totally optional : communication or not, BMS stops charge or discharge if out of specs ...

So, you set your inverter up for two batteries, one developes an issue and stops charging. Now the other one gets overcharged and also trips. System down. That is a poor design.

8 hours ago, deonholt said:

I forgot to mention: The question is with regards to lead-acid batteries. It has the same 180AH rating, both 12V & both lead-acid. Can I use them together in series?

No issue doing that as long as the bulk and float voltages for the two ore more batteries are about the same.
A battery balancer/equaliser would be recommended though for such an installation.

https://sp-energy.co.za/product/battery-balancer-ha02/

Edited February 9, 20233 yr by zsde

11 hours ago, frivan said:

So, you set your inverter up for two batteries, one developes an issue and stops charging. Now the other one gets overcharged and also trips. System down. That is a poor design.

Right ... Except there is no reason a battery module gets overcharged because the other one would have stopped charging. Batteries BMS limits voltage & current for each batteries independently.

If one battery stops charging, the other one will only accept voltage & current within limits of its BMS. Same for discharging : within the limits of each battery BMS.

If load > battery capacity : use candle. Communication between inverter & BMS does not change the problem ...

The only way to solve that issue aka good design is oversizing. If ever batteries may develop such issue ... Which is unlikely when the only job of a BMS is to not allow over or under charging or discharging.

Edited February 10, 20233 yr by zivva

3 hours ago, zivva said:

Batteries BMS limits voltage & current for each batteries independently.

It does not quite work like that. The BMS cannot control current flow, only prevent it, or request a value from the inverter, but the last feature only works if a battery is connected with comms to the inverter, and obviously not if the two have incompatible BMSs.

There is also definite ways to setup BMS parameters so that they will not ever work well together, regardless of whether there is comms.

For that reason almost all manufacturers clearly state that the warranty is void when paralleled with batteries from other brands (either in the manual or warranty).

19 hours ago, deonholt said:

I forgot to mention: The question is with regards to lead-acid batteries. It has the same 180AH rating, both 12V & both lead-acid. Can I use them together in series?

Are they both the same style, i.e. low maintenance, gel,  regular 'top up' batteries or sealed?

Also why? Are you replacing an old dead battery and keeping an old working battery, or just 2 different makes but both new?

It's not recommended to add new batteries to old batteries as the old battery will tend to drag the new battery down.

If they are both new, both the same style and both the same Ah rating then you should be fine.

18 minutes ago, P1000 said:

It does not quite work like that. The BMS cannot control current flow, only prevent it, or request a value from the inverter, but the last feature only works if a battery is connected with comms to the inverter, and obviously not if the two have incompatible BMSs.

There is also definite ways to setup BMS parameters so that they will not ever work well together, regardless of whether there is comms.

For that reason almost all manufacturers clearly state that the warranty is void when paralleled with batteries from other brands (either in the manual or warranty).

You can setup your inverter to charge your batteries at 500A if the battery BMS only accept 50A, your inverter will send 50A. Communication between the inverter & the battery doesn't matter for that purpose.

Communication between batteries allows to balance charge when 1 battery is full & the other not yet. Current flows between batteries instead of having the full battery not accepting any more current & the not yet full battery being charged by the inverter.

In theory you could connect all your batteries without any com between them or the inverter, still each BMS of each battery would close their MOSFET when cells voltage reach the BMS limits of charge or discharge. No way to monitor what is happening then but it would work.

The only reason manufacturers don't want customers to use different brands in parallel is because they want to sell you more batteries. As long as all batteries are of the same voltage (48v or 51.2v), no problemo ...

11 minutes ago, zivva said:

You can setup your inverter to charge your batteries at 500A if the battery BMS only accept 50A, your inverter will send 50A. Communication between the inverter & the battery doesn't matter for that purpose.

Communication between batteries allows to balance charge when 1 battery is full & the other not yet.

That is patently incorrect on both those counts.

3 minutes ago, P1000 said:

That is patently incorrect on both those counts.

 

19 minutes ago, zivva said:

You can setup your inverter to charge your batteries at 500A if the battery BMS only accept 50A, your inverter will send 50A. Communication between the inverter & the battery doesn't matter for that purpose.

Communication between batteries allows to balance charge when 1 battery is full & the other not yet. Current flows between batteries instead of having the full battery not accepting any more current & the not yet full battery being charged by the inverter.

In theory you could connect all your batteries without any com between them or the inverter, still each BMS of each battery would close their MOSFET when cells voltage reach the BMS limits of charge or discharge. No way to monitor what is happening then but it would work.

The only reason manufacturers don't want customers to use different brands in parallel is because they want to sell you more batteries. As long as all batteries are of the same voltage (48v or 51.2v), no problemo ...

 

Correct, you can set up your inverter to charge your batteries at 1000A if it has that capability but if your battery is rated at 50A charge then BMS will only allow 50A, even when there is no comms between the battery and the inverter. 

28 minutes ago, P1000 said:

That is patently incorrect on both those counts.

Maybe you should try ... And learn something

I suspect who is right and wrong will depend on a specific lithium battery's features. I know you get batteries with balancing, charging circuits, charge limiting, mosfets and all sorts of protection. However, I suspect you get batteries without these features and with limited protection. 

27 minutes ago, frivan said:

I suspect who is right and wrong will depend on a specific lithium battery's features. I know you get batteries with balancing, charging circuits, charge limiting, mosfets and all sorts of protection. However, I suspect you get batteries without these features and with limited protection. 

For now, lets forget about Gel batteries. The focus is on Lithium batteries with BMS, it doesn't matter which brand as long as it has battery management system, the charging current will be managed with or without comms between inverter and battery. That is the job of the BMS to do that and not the inverter. Communication is a nice to have but not a must 

2 hours ago, Acuario said:

Are they both the same style, i.e. low maintenance, gel,  regular 'top up' batteries or sealed?

Also why? Are you replacing an old dead battery and keeping an old working battery, or just 2 different makes but both new?

It's not recommended to add new batteries to old batteries as the old battery will tend to drag the new battery down.

If they are both new, both the same style and both the same Ah rating then you should be fine.

Both are new. I moved from a 24V to a 48V inverter. Supplier doesn't have same brand in stock of the 24V system. Both are lead acid & both 180ah.

13 minutes ago, deonholt said:

Both are new. I moved from a 24V to a 48V inverter. Supplier doesn't have same brand in stock of the 24V system. Both are lead acid & both 180ah.

Yes you can mix two different brands of Lead acid batteries. The voltage of both batteries is the same, put them in series and you will get your 48V

5 hours ago, hoohloc said:

 

Correct, you can set up your inverter to charge your batteries at 1000A if it has that capability but if your battery is rated at 50A charge then BMS will only allow 50A, even when there is no comms between the battery and the inverter. 

BMS cannot limit current, only cut off completely.

19 minutes ago, P1000 said:

BMS cannot limit current, only cut off completely.

well, it does that on my Pylons mate. I'm talking from experience here. My inverters are set to 140A each, making the total 280A. I have 5 x US2000 and 1 x UP5000 and not even once have I exceeded 175A. I have no comms between my inverter and the battery bank, the charge current is high in the morning, max I have see is 120A,  when the batteries are at around 40% and gradually reduces as the SoC approaches 100%. At 100% they stop charging and start discharging. Also, the inverter will only provide what the load demands. Meaning, you can set it to 500A charging current but if the load only demands 50A charge, that is what you will get. 

Edited February 10, 20233 yr by hoohloc

21 minutes ago, P1000 said:

BMS cannot limit current, only cut off completely.

See attached Seplos BMS manual about current management by the BMS. All BMS manage charge & discharge current. Inverters just do what BMS demands ...

I agree with P1000.Contrary to what many think, the BMS does not change the charge or discharge current, it really is just an on-off switch; if you have a charging source that can push hundreds of Amps into the battery the BMS will sense this, and switch the battery off when the upper safe limit is reached!

Edited February 10, 20233 yr by TaliaB