This popular smart charger is under $100 once again. Highly recommend them!
There is also 30% off the XS0.8 for $69 and MXS7 for $199 but I think the MXS5 is the best value.
Description from website:
CTEK MXS 5.0 - Automatic charger for car batteries
The MXS 5.0 is an advanced battery charger with a microprocessor giving unrivalled performance for charging lead acid car batteries from 1.2Ah to 110Ah. The MXS 5.0 comes with built in automatic temperature compensation ensuring the best charging performance of your car battery, even in the extreme weather conditions Australia throws at it.
The MXS 5.0 has some premium features including a battery diagnosis faction to detect whether your battery can actually receive and retain a charge. A patented function for automatic desulphation, An AGM option which can maximise life and performance of most Stop Start car batteries. Recondition mode for reconditioning and detoxing deeply discharged batteries for greater longevity. Like most CTEK battery chargers, The MXS 5.0 uses the patented float/pulse mode, which is the most efficient maintenance mode especially when a battery is connected up for longer periods including trickle charging your classic/weekend car. CTEK offers battery chargers for car batteries, boat batteries and motorcycle batteries for professionals and consumers.
With the latest advancements in intelligent battery charging technology, CTEK are committed to maximizing battery performance with every product they offer. Constantly pushing the boundaries of research and development, CTEK have soared leaps and bounds above the competition because they constantly innovate, improve, and refine to your needs and battery charging applications. A 12 volt battery charger is an absolute must-have for those storing project cars which only see the road or track once in a blue moon, since batteries naturally discharge over time when left to sit without a charge applied to them, your battery's health is severely compromised if its only given time to charge every so often.
CTEK battery chargers great for restoring charge to totally flat batteries when they would otherwise end up in the tip which means they're friendly to your budget and for the planet. A CTEK car battery charger is also great for maintaining battery charge to occasional vehicles such as project cars, weekend cars, boats, jet-skis, RVs or anything you can think of so you can be sure your car, bike or boat will fire into life at the drop of a hat.
I think you need a solar battery charger. Otherwise you're inverting to ac, then converting it back to DC.