Which MBA do you have? I love mine (11") and I need to replace the battery too, I think the last time I checked they cost about £50 
It was actually DHH that got me to try an 11" MBA, I fell in love with it and it quickly replaced my Mac Pro as my main workstation 
I love TextMate too! If I am editing a single file I will usually open in TM. I wish they had split windows like MacVim tho! They did say they were going to add them, but they never arrived 
