if you call fisher price you can purchase one over the phone. i ended up gettin a deal i got a battery and charger for $45 !! which is hella expensive but the charger itself is $30 and the battery is $25 so i got them both for cheap.
I picked up a charger from Radio Shack (same voltage etc.) but the plug did not fit. On another sight I saw someone with a similar situation and they purchased a universal charger. I bought the one they suggested and it works great! You can also read some of the reviews and people mention using it for Spike as well. It charges the battery using aligator clips and it very easy to use. I purchased it up on Amazon it was the Tenergy Universal Smart Charger for Nimh/nicd Battery Pack. Hope this helps!