Starting bank charging despite being isolated

[dluks]

I have a house bank and a starting bank, both of which can be isolated using a common four-position battery switch (OFF, 1 [house], BOTH, 2 [start]). I have solar connected to a Victron SmartSolar charge controller which has its negative lead connected to the main DC negative bus (to which both the house and starting banks ground to) and its positive lead connected to the "1" post of the battery isolator switch, [I]i.e. the battery side of the house circuit at the switch[/].

In theory, unless I'm fundamentally misunderstanding something, the charge from the charge controller, when the battery switch is set to house, should only be going to the house bank. My issue is that the starting battery's voltage nearly mirrors the house bank's when charging, e.g. 14.6V when in absorption. Again, the positive lead from the charge controller is connected to the switch on the battery side of the house circuit, not to the common post. I don't have a current-monitoring system in place so I'm relying on voltage readings for now.

My first guess is that the switch may be faulty and therefore when at the house position it is actually paralleling the two banks? Or could it be some stray current stuff (of which I'm woefully uneducated) due to the batteries being wired to the same negative bus?

The two banks consist of different batteries (house uses two 12V deep-cycle Trojans and start uses a single 12V dual-purpose Bruteforce, and so my worries are that, if paralleled, one bank will be consistently under- or overcharged. I also don't have a great regulator for the alternator (which is wired to the common post of the switch), and so I generally pop the switch over to only the starter when starting and running the engine to avoid improperly charging the house bank.

[dluks]

Solution: Turns out the echo~charge line running from the inverter/charger to the start post on the battery switch appears to have been the culprit as it was paralleling the banks. Switching off the main inverter/charger switch opens that circuit and the starter battery is no longer receiving charge current from the solar charge controller.

[smac999]

the echo charger was probably acting as an echo charger. that's what it does. charges the 2nd bank. (though I never thought or knew it worked from any source, I thought it was only when the inverter / charger was charging, but maybe it does, an external echo charger charges a 2nd bank from any charge source)

that line is also what charges the engine battery from shore power.

as long as it's not draining the house into the engine when the house is not charging, (under 13v) then I would leave it