What is this white substance on my car battery?
Car batteries sometimes emit a white or blue crystallisation around the posts as a result of the battery acid leaking to the atmoshere. This in itself is not always an immediate problem, but over time will corroded the post clamps and wiring and eventually may cause starting problems. The quick solution is to pour boiling water over this area dissolving the contaminant, apply and little grease or Vaseline and keep a regular check to see if it returns.
If the problem persists, it may be worth considering a replacement battery.