Additional idea, it would be cool to change the text colour according to the battery level...:
magenta/blue for high levels (00FFFF)
below 50% or so green (00FF00)
below 25% or so yellow (FFFF00)
and below 10% or so red (FF0000)

Getting the battery percentage is as easy as
lshal | grep percent
which on my device tells me:
battery.charge_level.percentage = 49 (0x31) (int)
perhaps there's an easier way, reading a file from /proc or so (I have 0 skill with python, no idea how to incorporate the above lshal command into this script).

Note also that green will render the sharpest text (I put longer quotes so I use a smaller font for things to fit).