Re: 12V DC to AC converter
If, frequency will not your criteria, purchase a transformer of 12 volt, 500mA step down center tap type from 230 Volt. Feed positive of battery to center tap of 12 volt, base Resistance, 1K, 1W, Capacotor 10µF, 63V. Power up and check the output. Mind it, being isolated, Neon tester must not glow on one side, until you ground the other side. Dont forget to use heatsink to your 3055 like power transistor.
Hope it solve ur problem. The output can give upto 10 Watt depending on the operating frequency.