Skylla IP-44 won't switch to absorption

Had a similar head-scratcher on my narrowboat last summer — Victron Skylla IP-44 sitting stubbornly in bulk mode like it had no intention of ever moving on with its life.

Turns out my battery voltage sensor cables had developed a dodgy connection at the terminal block, so the charger was seeing artificially low voltage and just kept shovelling amps in, never convinced it had reached the absorption threshold. Worth checking those first if yours is doing the same.

A few other things worth ruling out:

• Temperature compensation throwing the target voltage way up if your temp sensor is reading incorrectly (mine was sitting in direct engine-room heat)
• Battery capacity setting — if it thinks you've got a massive bank, the bulk phase takes an age
• Firmware — mine was on an ancient version, a VictronConnect update via the MK3-USB interface sorted a gremlin or two

My setup is a 200Ah AGM bank (Fogstar ones, solid so far) and a small Honda generator, so I only run the Skylla occasionally like yourself — which I reckon means these chargers sit unused long enough for settings to feel like a mystery when you come back to them.

What battery type have you got it configured for? Flooded, AGM, or custom profile? That's sometimes where the rabbit hole starts — someone's set a custom voltage profile and forgotten about it entirely.

Anyone else on here had the Skylla refuse to leave bulk? Curious whether it's more common than Victron let on. 🔌

@SussexBoater classic Victron gotcha that one — the Skylla's absorption threshold is calculated as a percentage of programmed battery capacity, so if your capacity setting is way off, the charger thinks it hasn't delivered enough amp-hours yet and just... keeps going.

Worth checking:

• VEConfigure — is your battery capacity set correctly?
• What absorption voltage is configured? For AGM typically 14.4V, flooded 14.7V
• Any chance you've got a dodgy battery temperature sensor? Cold readings fool it into staying in bulk longer

I've got a Skylla IP-44 on my LDV Convoy conversion and had similar grief until I realised my bank capacity was programmed at 100Ah when I'd fitted 200Ah of Fogstar Drift. Charger was waiting to deliver twice what it thought it needed before transitioning. Five minute fix once you know!

Good shout from both of you. Worth adding — if you're running lithium (Fogstar Drift or similar), double-check your absorption voltage is actually set correctly for the chemistry. The Skylla IP-44 defaults to lead-acid profiles out of the box, and if someone's nudged the bulk/absorption voltage gap too narrow in VictronConnect, it can look like it's stuck in bulk when really it just never reaches the threshold.

Also had a weird one on my van build where a dodgy battery temp sensor was feeding false readings — charger thought the bank was warmer than it was and kept backing off current, so voltage never climbed high enough to trigger absorption. Unplugged the sensor temporarily and it transitioned fine. Narrowed it down pretty quickly after that.

Check the History tab in VictronConnect — it'll show max voltage reached during that session which tells you a lot.

Good points all round. One thing worth adding for anyone running a static setup or EV charging scenario like mine — check whether you've got a high-resistance connection somewhere in the battery cabling. I had the Skylla convinced it was still in bulk because the voltage it was measuring at its terminals was lagging well behind the actual battery voltage, due to a dodgy crimp on the negative busbar.

Quick test: put a multimeter directly across the battery terminals while the charger's running. If that reading is noticeably higher than what VictronConnect is reporting, you've found your culprit.

@CoveMick's lithium point is worth heeding too — absorption onset voltage for Fogstar Drift cells needs to be set conservatively or you'll trigger BMS protection and the charger just sees a disconnect.

Great thread, this caught me out too on my off-grid cabin setup. One thing nobody's mentioned yet — check your battery temperature sensor if you've got one fitted. Mine was reading a false high because the sensor had worked loose and was sitting in warm air rather than against the battery casing. The Skylla was compensating by dropping the absorption voltage target, which meant bulk never quite reached it. Reseated the sensor with fresh thermal paste and proper cable tie, and it transitioned to absorption within minutes. Worth also having a look in VictronConnect at the charger history tab — it'll show you the actual voltage curve over time, which makes it much easier to spot whether you've got a voltage or current threshold issue. Often saves a lot of head-scratching.

@OwenYoung83 raises something I hadn't thought to mention — good spot on that.

Something else worth checking if you've exhausted the obvious culprits: the absorption voltage detection window. The Skylla IP-44 uses a voltage rate-of-rise algorithm to judge when to transition. If you've got a long cable run with meaningful resistance, the charger may be "seeing" a falsely elevated voltage at its terminals — making it think the battery is already near absorption, but then not quite hitting the threshold cleanly, so it just... stalls in bulk indefinitely.

Ran into exactly this on my shepherd's hut setup with a 4m cable run that was slightly undersized. Bumped the conductor cross-section to 16mm² and the behaviour sorted itself immediately.

Worth measuring voltage at the battery terminals versus at the Skylla output simultaneously — any significant delta is your answer.