Victron MPPT 100/30 keeps showing absorption too early — anyone else had this?

Picked up a Victron SmartSolar 100/30 about three months ago to pair with my 200W panel setup (two 100W panels in series) on a static cabin setup in rural Wales. Generally really happy with it, but I've noticed something odd — it seems to be jumping into absorption stage way earlier than I'd expect, sometimes only an hour or so into a charge cycle even when the battery bank was sitting at around 60% SOC overnight.

Battery bank is 200Ah of AGM (two 100Ah Varta leisure batteries in parallel), and I've got the charge profile set to the manufacturer's recommended settings: absorption at 14.4V, float at 13.8V, with an absorption time of 2 hours. The thing is, it seems to hit 14.4V really quickly in the morning and then just sits in absorption for ages without the current dropping much, which makes me think it's not actually full when it claims to be entering that stage.

I've had a poke around in the VictronConnect app and I'm wondering if my tail current setting is off, or whether the panel voltage is somehow spiking and fooling the controller. Has anyone experienced similar behaviour with the 100/30 specifically, or with AGMs in general? I'm also wondering whether the Welsh weather (read: relentless cloud and drizzle) is somehow causing weird charge patterns compared to a more straightforward sunny-climate setup.

RetiredNurse96 | 847 posts | ⭐ Trusted Member

@AndreaHamilton Ooh, Wales — so you'll know all about those overcast days! One thing worth checking that caught me out: make sure your battery temperature compensation is set correctly if you're using the VictronConnect app. I had my absorption triggering early on my setup because the controller was reading a warmer ambient temperature than reality, which fooled it into thinking the batteries were fuller than they were. Also worth double-checking your battery capacity setting in the app — if it's set too low, the algorithm cuts to absorption sooner. What battery type are you running? AGM, lithium, or flooded lead-acid? Makes quite a difference to how the controller behaves. Mine took a good few weeks of fiddling before I got it properly dialled in, so don't despair! 😊

PYQ_Power | 1,203 posts | ⭐ Trusted Member

@AndreaHamilton Worth checking your battery capacity setting in the VictronConnect app — if it's set too low, the controller thinks it's reached absorption threshold sooner than it actually has. Also, what battery type and capacity are you running? The default absorption voltage for AGM sits around 14.4V, but if you've got lithium or a non-standard AGM bank, you might need to tweak the charge profile manually.

Three months in is actually a good time to catch this — sometimes the default settings ship configured for smaller banks. Have a look under Battery Settings > Charged Voltage and cross-reference it against your battery manufacturer's spec sheet. Five minutes in the app usually sorts it. What does your battery history tab show for typical absorption duration?

SueThompson99 | 312 posts

@AndreaHamilton I had almost the exact same issue with my 75/15 last summer. Worth checking what your "tail current" is set to in VictronConnect — it's the percentage of charge current at which absorption ends early. If it's set too high, the controller thinks the battery is full before it actually is. Mine was defaulting to 4% and dropping into absorption far too soon. I knocked it down to 1% and it made a noticeable difference. You'll find it under the charger settings once you're connected via Bluetooth. Takes about 30 seconds to adjust. Might be worth doing that before anything else rather than diving into more complex settings. 🙂

KateMason82 | 156 posts

@AndreaHamilton I had this with my 100/20 last year — worth having a look at your wiring resistance between the controller and battery. If there's any significant voltage drop along that run, the controller "sees" a higher voltage at its terminals than what the battery's actually at, so it thinks absorption threshold has been hit earlier than it should be. Even a few millivolts can throw things off with AGM or lithium profiles. What battery type are you running and how long is your cable run? Also, are you using the Victron app to monitor — if so, check whether your absorption voltage target actually matches your battery manufacturer's spec, as the defaults aren't always spot on out of the box.

VivaroWanderer | 2,156 posts | ⭐ Trusted Member

@AndreaHamilton One thing nobody's mentioned yet — check your battery temperature sensor situation. If you're running without a SmartSense or BMV-connected temp sensor, the MPPT assumes a fixed 25°C. In a Welsh cabin through autumn/winter, your battery bank could genuinely be sitting at 8-10°C, which significantly affects the absorption voltage threshold and makes the controller think it's hitting targets it hasn't really reached.

Running a Victron SmartSense on my Vivaro setup transformed the charge curve accuracy completely — went from similar early absorption symptoms to properly full cycles.

Also worth double-checking your battery voltage sense — if it's only reading at the controller terminals rather than directly at the battery, any cable voltage drop will fool the algorithm.

What chemistry are you running? AGM and LiFePO4 profiles behave very differently in cold conditions.

OldSailor86 | 847 posts

@AndreaHamilton Had this exact head-scratcher on my narrowboat a couple of winters back. Turned out my battery temperature was the culprit — the Victron was compensating for what it thought was a warmer battery than reality, pushing it into absorption prematurely.

If you're running the SmartSolar without a Smart Battery Sense or temperature sensor connected, it defaults to 25°C. A rural Welsh cabin in autumn? Your batteries are probably sitting at 10-12°C, which completely throws the voltage calculations off.

Grab a Battery Sense (they're not expensive) or at least enable temperature compensation properly in the VictronConnect app. Made an enormous difference on my setup once I sorted it.

Also worth double-checking your battery capacity setting in VictronConnect — if it's underestimated, absorption triggers far too soon.

ExChippie | 634 posts

@AndreaHamilton Worth checking your absorption voltage threshold in the VictronConnect app — the default is often set too low for the actual battery chemistry you're running. Had this on my motorhome setup with a Fogstar 100Ah LiFePO4. The MPPT was seeing a slight voltage spike on a warm morning and jumping straight to absorption.

Also — two 100W panels in series means your Voc could be pushing 45V+ in cold Welsh mornings. That's fine for the 100/30 but make sure your charge profile actually matches what's in the battery. What chemistry are you running?