Batch RBF transactions (Electrum)

[Robot1982]

Does somebody know what this settings does? I know what RBF means, but I don't know what this "batching" means or how it works. Can somebody please explain this? Or is this documented somewhere? Thanks!

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[Rath_]

Does somebody know what this settings does? I know what RBF means, but I don't know what this "batching" means or how it works. Can somebody please explain this? Or is this documented somewhere? Thanks!

If the transaction hasn't been confirmed yet and you decided to create another transaction then instead of two separate transactions you would have one transaction with the inputs and outputs of both transactions. This feature lets you save a little on the fees.

[Robot1982]

Is this done automatically when I create the second transaction? Does it mean that whatever fee I choose for the second transaction will be actually for both transactions? I have to test this.

[Rath_]

Is this done automatically when I create the second transaction? Does it mean that whatever fee I choose for the second transaction will be actually for both transactions?

It happens automatically if you turn on RBF and RBF Batching before sending the first transaction. I'm not sure about the final fee but I guess the second transaction overrides it.

Down: That's a given. I have no idea why I was overthinking it.

[khaled0111]

I'm not sure about the final fee but I guess the second transaction overrides it.

Logically the second transaction must pay more fees, otherwise miners will pick the first one from the mempool. So yes. Second transaction fees will be applied.

[Robot1982]

Logically the second transaction must pay more fees, otherwise miners will pick the first one from the mempool.

This can be a problem if the miners pick the first transaction (for example if the second transaction has the same fee (sat/byte) or for some other reason), then the second transaction is not valid anymore and it will fail and you have to redo the second transaction. If you want to make sure that this doesn't happen, then you have to set a higher fee for the second transaction which will negate the benefit that the "batch RBF transactions" has in the first place (save some fees). This may still work if you only slightly increase the fee for the second transaction but still you cannot be sure that this transaction will be confirmed first.

[nc50lc]

-snip- This may still work if you only slightly increase the fee for the second transaction but still you cannot be sure that this transaction will be confirmed first.

Don't you worry, Electrum implemented RBF with accordance to the rules (wiki) otherwise, RBF transactions won't be accepted by the server (nodes) to begin with.
(except in some cases: bug)

Without clicking the link, #2 in the list indicates that the replacement transaction should pay additional fee of at least the minimum tx fee based from its 1sat/B fee rate,
ex: If the new RBF tx is 295bytes, then it must pay at least 295sat higher than the original tx; same with batching, but the minimum additional fee will be based from the batched tx.

TL;DR: You'll never be able to create a replacement TX with lower fees as it will be rejected by nodes.