Before you go spending a fortune on a new batery, try re-setting the ABS.
This is the technique..it'll only take a few mins and it's free
(originally posted by Migsel
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1) Turn ignition off.
2) Remove the seat.
3) Locate the diagnostics plug behind the battery.
(It's for diagnostics so is not connected to anything).
4) Connect an end of wire to the brown/blue wire pin .
5) Clip the other end firmly to ground.
6) Turn ignition on. Note that the two ABS lights continue flashing alternately.
7) Hold ABS button down for 8 seconds.
The bottom ABS light should stay on, the top one off.
Release the ABS button.
8) If the reset is successful, both ABS lights come on.