The engine spurt is probably caused by a cell phone or some other 27mhz radio interference. It's common, many people have reported it in this thread and I've experienced it a couple times. I just switch the plane and TX off as soon as I quit flying. If the bird ends up in a tree and needs a retrieve (a common experience whenever the wind picks up above a breath), I always switch off the TX just to save the batteries. Keeps me in the habit of conserving power.

Re the batteries, microbuilder and others in this thread have discovered it's a little lipo battery. They'll last a long time, but like any rechargeable, they'll wear out in time. Someone suggested recharging your plane if you've run it more than a minute and a half, just to keep the battery in good shape. I don't know much about lipos, though I have a few for various models I'm building, so I can't say from personal experience.

Doing a search in the right forum will I'm sure give you more info than you ever thought possible on that and any other subject...this is such a great website. Also, RC Groups (rcgroups.com) has a wonderful, extensive forum, in case you don't know that one, with a wealth of information.