Car wont hold a charge.

I have a 1997 isuzu rodeo, v6. I was driving down the free way a little over a week ago when my car just started to lose power. My car died but luckily I was able to jump it to get it home. I took my car to checker to have the battery checked and the alternator checked, it turned out my alternator was bad. I replaced my alternator and my battery and the car started up fine and appeared to be working correctly, but after I began to drive it, the same thing happened again. The battery is holding really low voltage, only about 10 volts. Also I i stopped my car in a parking lot, and when I released my foot off the break my car began to accelerate on its own, it reached 25 mph with out me even touching the gas. Im very confused what do I do?