Charge de batterie incomplète

Been having a similar head-scratcher with my setup lately and wondering if others have hit the same wall.

During the recent hot spell we had, my Victron SmartSolar seemed to be cutting absorption short — battery wasn't reaching full SOC even on decent solar days. At first I thought it was the panels underperforming in the heat, but actually I think the controller was throttling back because the battery itself was getting warm sitting in the garden office (no real ventilation in there).

A few questions I'm trying to work through:

• Does anyone actively monitor battery temperature compensation on their MPPT? I've got a Fogstar Drift LiFePO4 and I'm not 100% sure the temp sensor is even giving accurate readings through the Victron app
• Is absorption voltage worth tweaking manually during summer? Or is that a rabbit hole best avoided?
• Could the EV charging I run off the same bank be partly to blame? I wonder if the battery's never getting a proper rest before the solar cycle kicks off again at dawn

I've ordered a small USB fan for the office space to see if just keeping air moving helps, but it feels like a sticking plaster rather than a proper fix.

Would be curious whether anyone's using the Victron VRM portal to actually log these charge cycle anomalies over time — I can see some data but I'm not sure I'm pulling the right metrics to diagnose this properly.

Anyone else noticed charge behaviour going a bit odd over summer? What did you do about it?

@LazyWarden yes, classic summer frustration this one! My SmartSolar was doing exactly the same thing parked up in the Lake District last July.

What caught me out was the temperature compensation working against me. When the battery bank (Fogstar 200Ah lithium) gets warm sitting in a hot van, the MPPT actually lowers the target voltage — so absorption ends earlier than you'd expect.

Worth checking in the VictronConnect app whether you've got temperature compensation enabled and what coefficient it's set to. For lithium especially, some folk just disable it entirely.

Also check your absorption time settings — if it's set to a fixed time rather than adaptive, a partially cloudy morning can trick it into thinking the battery was already nearly full before the real heat kicks in.

What battery chemistry are you running?

Worth adding a detail neither of you have mentioned yet — high ambient temperature affects the battery temperature compensation.

If your SmartSolar is using a BMV or Smart Battery Sense for temperature readings, it'll actively lower the target voltage on a hot day. That's by design, not a fault. Lead-acid chemistry particularly benefits from this, though LiFePO4 setups handle it differently.

On my narrowboat last summer, moored in full sun for a week, I had exactly this confusion. Turned out the Smart Battery Sense mounted near the engine bay was reading artificially high temperatures — skewing everything.

Worth checking:

• Where your temperature sensor is physically located
• Whether temperature compensation is actually enabled in VictronConnect
• What your compensation coefficient is set to (mV/°C/cell)

The Victron documentation covers this properly, though the relevant section is buried a few pages deep.

@CraigCross is onto something — Victron's temp compensation default is -16.2mV/°C for a 12V system, so on a 35°C day your absorption voltage target quietly drops by nearly half a volt before you've even noticed.

Worth checking in VictronConnect whether you've got a Smart Battery Sense or BMV temp sensor feeding actual battery temp, otherwise it's just guessing ambient — which on a motorhome roof in summer is a completely different world to the battery compartment.

Also: absorption time cutoff. If your Victron's set to end absorption when tail current drops to say 2% of capacity, and your ageing cells have higher internal resistance, it'll bail out early thinking the battery's full when it absolutely isn't.

Fogstar Drift LiFePO4 cells have tighter tolerances here — sorted mine out completely once I recalibrated the charge profile properly.