The charger is a float charger you can get from Harbor Freight for around $15. They go on sale regularly and google the 20% coupon you can use as well. Float chargers won't damage the battery by constantly charging.
The only hard part to get is a 1.3mm jack. I found an old phone charger that fits the 1.3mm jack on the Vortech. You can always purchase the jack from Vortech. Splice the wire and one is positive (middle jack) the other wire is negative.
Costco has the cheapest auto battery with a decent warranty. Since most of the Costco batteries were the same price I chose one that fits my car. That way if my car battery dies I have a spare.
Here is a short diagram