LiFePO 12V batteries in series

[CL*]

Hi all -- I wanted to see if anyone knows the chemistry behind why SOME Li ion 12V battery packs don't have to be balanced when placed in series with each other to make 24V or 36V. Apparently you can just top each battery off to the same SOC before connecting them and they're good for a year. None of the manufactures actually tell me chemically why this is okay when BMS is so important inside the battery packs.
Trying to figure out if it's worth it to cheap out and not buy an extra external BMS or to not trust the seller and go ahead to buy one for safety. Can anyone explain it to me? Thanks!

 

[MisterSandals]

Apparently you can just top each battery off to the same SOC before connecting them

Which Li ion battery packs are you referring to? Do any of them actually have a way
to balance the cells and to check the state of the cells' balance?

buy an extra external BMS

Are you considering putting a BMS on 3 battery packs in series (of which each probably has its own internal BMS)? I cannot imagine how this would work or why someone would try it.

 

[Ampster]

I wanted to see if anyone knows the chemistry behind why SOME Li ion 12V battery packs don't have to be balanced when placed in series with each other to make 24V or 36V.

I don't think it is a chemistry issue. A more detailed explanation would depend on each manufacturer and how they implement serial connections if at all.

 

[CL*]

Hi all, Sok's batteries (and Battle Born's) are advertised to have BMS systems in their 12V units and the sellers say they can be safely placed in series without an external BMS. I keep pressing them to tell me why -- do their internal boards communicate externally between batteries? Neither manufacturers can tell me how multiple 12V batteries is safe besides "just set it up correctly first and you'll be fine"... they just don't seem to know the answer themselves, so I'm trying experts on this forum!

 

[CL*]

Which Li ion battery packs are you referring to? Do any of them actually have a way
to balance the cells and to check the state of the cells' balance?


Are you considering putting a BMS on 3 battery packs in series (of which each probably has its own internal BMS)? I cannot imagine how this would work or why someone would try it.

Yes, actually, I was wondering why we wouldn't need another balancer with multiple "smart" batteries in series. Why exactly wouldn't this work? I think that's the question I'm muddled about.

 

[MisterSandals]

I was wondering why we wouldn't need another balancer with multiple "smart" batteries in series.

Now you're talking about balancers which is not the primary function of a BMS in my mind.

Its an interesting thought that batteries would need balancing while in series. It would take
a 36v 3S balancer (or BMS with balance function)... which is unlike anything I've seen.