My mobility scooter has a 270W motor. It operates with two 12V 12AH batteries. The battery charger works only with 110 current. Voltage converters seem to be rated by watts. What capacity voltage converter would I need to purchase to recharge my batteries in Europe? I don’t want to tote around any more bulk or weight than necessary. Same question for a 450W scooter.
My charger is 2amps.

Rascal, your main question is the minimum capacity to charge those 2 batteries, and how long that it will take. Generally, chargers are rated at a volts and amps rating. I’m willing to bet that your 2 batteries are wired in series. You would need a charger that supplies at least 27 watts, or 1.2 amps, at 24 volts.
Now, let’s change this around a little bit and get something that you don’t need an electrical outlet for, and would go just about anywhere that you want to go. Look up “fuel cells”. These nifty devices are small, but can charge your battery litterally anywhere, so long as you have fuel to power it. Generally they use propane, so a 1 or 2 pound cylinder would provide easy power to recharge your batteries. This means that with a little planning, you would be free to explore where you would never consider going before. The fuel cell burns a fuel, with air, and creates electricity. What I have seen, and asked about are fairly small, but can deliver the voltage, and current that you need. Their efficiency is over 85% for energy in, versus energy out.