User Defined charging Parameters for the IP65 12/7

This is something I've been thinking about more lately, particularly as OEM lithium auxiliary batteries start appearing in newer vehicles and people try to use quality chargers like Victron's IP65 range to maintain them.

The IP65 12/7 has some user-defined modes, but the question is whether they give you enough granularity for NMC chemistry specifically. NMC sits in an awkward middle ground — it's not your standard lithium iron phosphate (LFP) that most of us run in our off-grid setups, and it's not traditional lead-acid either. Charge voltage ceilings tend to be lower than you might expect, and the absorption behaviour matters quite a bit for longevity.

My concern with using any charger in a maintenance/trickle role on an NMC pack is whether the float voltage is genuinely configurable to something the BMS will tolerate long-term without repeatedly topping off to a voltage the chemistry doesn't love. Fogstar and similar suppliers are quite open about this with their LFP cells, but OEM NMC packs in MHEV applications are a different beast — the BMS is often tightly integrated and doesn't always communicate what it's actually doing.

Has anyone here actually mapped out the user-defined profile options on the IP65 12/7 in detail? Specifically:

• What's the minimum configurable absorption voltage?
• Can float be set independently and low enough (say, 13.0 V or below)?
• Does the charger respect a BMS-triggered charge termination properly?

Would be useful to get some real-world numbers rather than just the spec sheet. Anyone running Victron kit on a modern OEM lithium auxiliary pack?

@CamperShaun this is really relevant to my van build actually — I've been scratching my head over exactly this.

Quick question for the thread: if the host vehicle has an OEM lithium aux (say, a Ford Transit Custom with the factory 12V lithium), and you're feeding a second leisure battery via the IP65, does the charger "see" the OEM battery's voltage at all, or is it purely reading from its own output terminals?

Wondering because I've got a Fogstar Drift 100Ah on the leisure side and I'm paranoid about:

• Absorption voltage being set too high
• The BMS cutting out mid-charge and the charger going haywire

Is user-defined mode on the IP65 actually stable enough for this, or does it still do that weird CV-phase hunting people mention? Anyone used it on a narrowboat 12V bank with similar concerns?

@CamperShaun worth noting that the IP65 has the Li preset locked at 14.2V absorption / 13.5V float which is fine for most LiFePO4 but some OEM packs — particularly the newer Ford Transit and VW ones — have tighter windows specified by the manufacturer.

I've got mine running to a Fogstar Drift 100Ah in my shepherd's hut setup and ended up using the "User" profile via the VictronConnect app to dial absorption back to 14.0V. Made a noticeable difference to how the BMS behaves under charge termination.

The app gives you full control but it's buried — Settings > Charger > Battery Preset > scroll to bottom. Don't rely on the default Li mode if your pack documentation specifies anything outside the standard parameters.

Anyone know if the newer Transit aux packs publish their actual charge voltage specs publicly? Can't find them anywhere.

@JA_Solar the "fine for most" doing a lot of heavy lifting there when some OEM packs throw a tantrum if you breathe on them above 14.0V 🔋

@MarineClare my boat batteries had a proper meltdown the first time I threw a non-tailored profile at them — "fine for most" is genuinely doing Olympic-level heavy lifting in that sentence.