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Rules for mixing batteries?

metalheaddoc

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Mar 12, 2022
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Kansas City, MO, USA
If I buy a 12v 100AhLFP battery from brand X, do I need to buy the same brand if I want to expand my battery bank? Or are the various brands interchangeable? Any rules for mixing and matching batteries?

Similarly, If I have two 12v batteries in series and I want to expand, can I add a 24v in parallel or would I have to add two series-connected 12v in parallel?
 
Generally batteries of the same chemistry should have same charging specs and go fine in parallel. Even different capacity.

In series I recommend same, same, same bought at the same time from the same supplier. Best with LFP is to get the higher voltage battery to match the components so the internal BMS can keep all in balance and avoid series issues.
 
The biggest rule is: the mixed battery voltages must be equal.

If you're an experienced person: Mixed chemistries are okay too. Of course, you need to add some extra devices.

Less important rule 1: choose equal capacity. There may be errors with different capacities, but the impact is not that big.

Even less important rule 2: Equivalent brands. There will be some differences in batteries between brands, but the difference is actually not that big. However, with the exception of batteries with built-in BMS, this can make a big difference.

Mixing different batteries is actually not too complicated. For your question, I think as long as your newly added battery is a 24V battery of the same chemical nature.
 
The biggest rule is: the mixed battery voltages must be equal.

If you're an experienced person: Mixed chemistries are okay too. Of course, you need to add some extra devices.

Less important rule 1: choose equal capacity. There may be errors with different capacities, but the impact is not that big.

Even less important rule 2: Equivalent brands. There will be some differences in batteries between brands, but the difference is actually not that big. However, with the exception of batteries with built-in BMS, this can make a big difference.

Mixing different batteries is actually not too complicated. For your question, I think as long as your newly added battery is a 24V battery of the same chemical nature.
To clarify the biggest rule: Does that mean all the batteries need to be 12v or that each parallel branch must be a 24v or 12v+12v equal voltages?
 
To clarify the biggest rule: Does that mean all the batteries need to be 12v or that each parallel branch must be a 24v or 12v+12v equal voltages?
Just the same voltage. Because your original battery pack is two 12V batteries in series, which is a 24V battery system. You only need to ensure that the parallel battery packs you connect in the future are all 24V, whether it is 12V+12V or a separate 24V.
 
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