You don't have to replace all your batteries just throw all the ones you have away and buy enough new ones to get you started .. Welcome back .. Go over your planes carefully ..If you can afford to upgrade to the new 2.4 system you will love it , if not what you have will get you buy for now .Your engines will be fine once you do some maint on them ..I would have a trusted instructor stand beside me for the first flight just in case ..Good luck ..