A broken or slipping drive belt linking the alternator, power steering pump & crankshaft pulley wheels could be a possibility - if it is this, your new battery will also soon go flat. The alternator is driven by the engine via this belt & provides electricity to power lights, heater fan, radio etc when the engine is running & also recharge the battery to replace power taken out of it when the car is started or when electrical power is used from the battery when the engine is switched off. Without this recharging process, the battery will gradually go flat. Adjustment or a new belt should cure battery & steering problems (the steering pump provides the power steering assistance) - Vauxhall dealer will obtain radio code for you.