I duel celled my microsizer by doing this duel cell mod http://www.endlesswaltz.net/bdrift/2batt.htm. I also modified my remote, but even before the remote was modefied, the car would go in reverse on its own. Also whenever i charge it on my stand alone charger or modded remote, it goes in reverse! Some times it will even start accelerating, and when i set it down it'll stop. can somebody please help!?
You have to make sure that the connections are clean. Your negaviter terminal is making contact with the first cell(original batt.) and you have to make sure you seal that battery up well. One idea is you can use some electrical tape on the original battery's negative side.
Hope this helps!