I have had issues with my truch starting at different frequencys, this happend a couple times over last weekend, also I can see corrosin around the terminals and have had to fill with water. The dealership said they couldnt find any problem, but this shouldn't be happening with a 2 year old battery. I had some issues with this when the truck was new.
Battery issues, not starting, losing water on 2009 Ford F-150
by Visitor in Guthrie Center, IA on April 14, 2011
ANSWER by torque wrench on April 14, 2011
Sounds like you are having a overcharge problem. May be intermittent, needs to be checked when cold, hot, and running a/c heat etc. The fact that you are getting corrosion around the terminals and having to add water, are sighs that battery is overcharging and boiling the water out.