MPPT addition to the system rises the voltage floor

Noticed something curious happening with my static caravan setup after I bolted a Victron MPPT 100/30 onto the existing system last spring.

Previously, running just the Multiplus II GX alongside a pair of Fogstar Drift 100Ah lithium batteries, once the bank hit full SOC everything settled down predictably — bus voltage would plateau nicely and the Multiplus would back off. Calm as a Lakeland morning.

Since adding the MPPT though, I'm seeing the bus voltage sit noticeably higher after reaching 100% — almost like there's a new floor that wasn't there before. The batteries aren't being overcharged (BMS logs look clean), but the voltage is holding maybe 0.3–0.4V above where it used to rest. On sunny afternoons with the panels still producing, it's like the MPPT is quietly insisting on keeping things topped up even when the Multiplus has already stepped back.

My working theory is that the two charge sources aren't fully negotiating absorption/float handoff in the way you'd hope. The MPPT seems to be anchoring the voltage upward on its own terms.

Has anyone else seen this after introducing a second charge source to a system that was previously inverter-only? Particularly curious whether folks running Dyness or similar "dumber" batteries without active DVCC communication have experienced the same thing — or if it's more pronounced when the battery BMS isn't fully talking to the Cerbo.

Worth adding: I've got DVCC enabled and shared voltage sense on, but I'm wondering if there's a setting I'm missing that would let the MPPT properly defer to the Multiplus once absorption is done.

@CumbrianWanderer this is the MPPT's absorption/float voltage reference fighting with the Multiplus II GX's own charge profile.

When both are active simultaneously, whichever device has the higher voltage setpoint essentially "wins" and pulls the battery voltage up to that level. The Multiplus then sees the battery as already at that voltage and backs off, but the floor never drops because the MPPT keeps compensating.

Fix: Enable shared voltage sense and synchronise charge profiles properly. On a Victron-to-Victron setup you should be using VE.Smart Networking via the VictronConnect app - the MPPT and Multiplus can then coordinate charging phases rather than working against each other.

Also worth checking your DVCC settings in the GX portal. With DVCC enabled and SVS/SCS ticked, the Multiplus takes control and the MPPT follows its lead. That's the intended behaviour for a combined Victron system.