There are a lot of misunderstandings out there about Echo's, Duo's (B2B's) and ACR/VSR relays. I suppose I need to write an article on this subject...
*Easiest installation and least additional installation expenses if charge sources already flow to HOUSE bank.
*Can mix some battery types, but not all
*Ideal & simple for just keeping a small start battery "topped up"
*Limited to 15A max
*Is a one-way device
*Could, in-theory, potentially
over charge a "start" battery if house bank stays at a high absorption for a long enough period of time (never seen it, likely due to the voltage drop).
*POS factory fuses & poorly executed crimps MUST be replaced
*Voltage limited to 14.4V and non-adjustable (Trojan's & US Battery prefer higher charging voltages than 14.4V)
*WILL-NOT do float independently of the house bank. The manual lies and misleads owners to believe it will. It is simply a voltage follower and follows the house bank minus any voltage drop.
*All charge sources MUST be wired to the HOUSE bank if not already wired as such. This little tid bit can make an Echo or Duo charger cost a LOT more than an ACR installation.
*Bi-Directional - current can flow equally both ways
*Bi-directional voltage sensing - turns on when either bank is charged
*Significantly higher current capability
*Both banks are charged at the SAME voltage thus both banks reach absorption, float etc. at the same time.
*Impossible to have one bank with a higher voltage than the other for more than the first few seconds
*Large studs (Blue Sea ACR's) allow MRBF bank fusing to be installed on ACR if close enough to bank
*Completely sealed/potted unit
*Better choice when owners decide to "alternate" house banks (this is not advised but people do it)
*Great choice for windlass or thruster banks (more available current)
*Requires more expense because wiring is significantly larger gauge
*Requires more expensive fusing
*Not the best choice for mixing battery chemistry
*Requires running alt to house bank if banks are of unequal sizes
*Requires the "start isolation" feature to be wired if solar or other change sources exist
The Echo is very often the easiest to install but not necessarily always the best choice. I install boat loads of both B2B's and VSR's it just depends upon the application.