Normaly, once the twizy is up, its up and everything will be powerd by the dc/dc. (trough the main battery)
But I agree with osbrook. If you havent replaced the battery you should do so.
14,8 is the max voltage the cicruit will provide.
If the12V is a goner and you have a short/or other way around , the charger may prevent the rest from functioning correctly.