Ah ok, so if I spend good $$ on a Battery, then I wont need the added on charger then .
I was typing on the phone while at work so I probably should have added more info to my original post. The DCC battery charges are useful when charging batteries that require a much higher voltage to be charged fully such as AGM and Calcium deep cycle batteries which tend to be the more expensive types of battery. Also, AGM batteries don't like a lot of amps so the battery charger limits the amps sent to the battery and can vary them depending on temperature and what part of the charge cycle. The charger can supply up to 15 volts (for Calcium batteries) while the alternator only does a max of 14.1 volts on my truck and not for long.
If you are planning on buying a hybrid battery similar to your starter as the second battery (Exide Extreme, Century Overlander etc.) then the battery isolator is all you need and maybe give it a charge with a 240 volt charger when at home. If you are planning on an AGM under the bonnet then a DC;DC charger is the go. About 2.5 years ago I needed a new auxiliary battery and was comparing a Century marine battery and a DEKA AGM battery from the US. Century was $199 and DEKA was $350 on sale. I wanted to try the new technology and went with the AGM. Then a few weeks later I decided to protect my new investment and bought a Redarc 1220 charger off ebay ($320) and installed it myself. In hindsight its not a cost effective way of doing it as the AGM is starting to show signs of not holding a charge as well as it used to. I have run the recondition mode on the battery with my c-tek but it has not made a difference. It still works but it needs to last a long time to pay itself off. The $199 wet cell battery (with the standard isolator that the car came with) would have been a much better and cheaper choice.
So the moral of the story is when you go to buy your battery know what chemistry type you want and the charging method. Simply looking at price and saying the higher the price or the more modern the chemistry type must mean it will last longer is not true.
EDIT - The advantage of an AGM battery is that it charges faster than a wet cell and can also be discharged to a lower state. It can also be used inside a car as it wont spill or vent acid. For an under bonnet install the wet cell is a better choice as it resists heat better and as long as you use the car regularly or top up with a solar panel then speed of recharge isn't an issue. In real life the difference in charge rate between the two types is negligible.
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