I wonder how 'intelligent' it is?
Votronic make a very similar item for the same money and you may be interested to see what it looks like inside ...
As you can see below...100% charging with everything off. The graph shows that I have just been for a drive and has been charging. Very accurate....drove to Tesco.....showing the rise in charge, levelled off whilst in shopping, then charging on way home, pretty pleased with it now.
www.t6forum.com
about £2 worth of components.
A lot of these units work on basic voltage differentials between the two batteries - so as long as the Leisure
Battery is around 0.7V higher than the Starter
Battery, the unit will turn on and a current will flow from LB to SB. That can generally work as a Starter
Battery is not typically below 12V and a Lead Acid
battery is usually only above 12.7V when on a charger (they will be higher for a while after charge, but when in use for a small time, the voltage drops of course).
So when all is good, those units are fine, UNLESS you have Lithium Batteries, where the voltage settles much higher and so there can be a constant transfer between LB and SB as the differential is over 0.7V and can remain so until the Lithiums are virtually drained.
Also, if a fault occurs on a
battery which creates a big drain (or if something is left on that is sucking the
battery down), as the SB keeps dropping, the >0.7V difference means that the LB - whether Lithium OR Lead-Acid - can get sucked down as well.
This graph shows how a
battery can go bad for no apparent reason - Look at the voltage (blue) line dropping as the
battery fails from around 2:00AM
View attachment 56081
Now if you had a simple
battery maintainer like the Votronics, potentially like the eBay one (I don't know the details of that but I suspect it is similar), or the wonderful 'Clive Mott' system that some like to promote, the effect of this fault occuring on a Starter
Battery would be to drain the Leisure Batteries to such an extent that they could likely be damaged beyond further use.
I personally would not fit one of those units in my van if I were given it for free unless I could be sure it would disengage at low voltages (and I mean
be sure, not just base the decision on a description in an eBay listing backed up with no data or tech sheet)