Join Date: Aug 2006
Location: Arlington, VA
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The Xantrex EchoCharge is designed to maintain a second battery, e.g., a start battery. It does this by stealing a bit of current, up to 15A, from the house battery bank whenever it senses a charge on that bank (i.e., whenever the voltage on that bank exceeds about 12.9VDC).
It will not overcharge your start battery. It is a voltage follower device, with pretty much the same profile as the main charger, but it has built-in smarts and will cut off when the attached battery is full.
The 15A maximum current of the EchoCharge has nothing to do with the amperage of your charger. You could have a 200A charger on the house batteries. The EchoCharge would sense a charging voltage, and would then steal up to 15A of that charging current to divert to the start battery...if it were needed. Usually, however, start batteries require very little charging current and a short time to reach full charge, because the act of starting the engine draws less than 1 amp hour from the start battery (high current while starting, but only for a few seconds).