Battery replacement with more powerful one

Thanks for your prompt answer.

No, I didn't yet planned the replacement, I'd like to do it because of the present autonomy doesn't achieve 4 hours, but just a question: why do you say that there is non big differences between the batteries of 2011 and 2013 MBA model? According to the specs, the new one has more than 5.000 mA and an autonomy of 8-9 hours, versus the 3-4 hours max of my one.

I'm wrong?

The life estimate is in a new machine. THere's more to battery life than a few extra mAh hrs of storage, as you will find out if you spend he extra $ for one. You're thinking is similar to thinking high test gasoline will make the average car run faster or get more MPG. It's flawed. there are tremendous architectural differences between the "2011 Mid-2012" and "Mid-2013" lines. the "Mid-2011" MacBook Air models are powered by "Sandy Bridge" Core i5/i7 processors, use integrated Intel HD Graphics 3000, and have 1333 MHz DDR3 memory.

The "Mid-2013" MacBook Air models are much more advanced with power conserving "Haswell ULT" Core i5/i7 processors with slower clockspeeds but a faster "On Package Interface" (OPI) that directly connects the processor and chipset, higher performance Intel HD Graphics 5000 that share 1 GB of memory with the system, 1600 MHz "Low Power" LPDDR3 SDRAM, faster PCIe-based flash storage,all that along with the larger batter is what extends the "battery life". Save a few dollars towards a newer box - buy the cheaper, proper, battery for your machine.