Absorption time is only for minutes with AGM battery

Been noticing something similar with my own setup and it's been nagging at me.

Running a Victron SmartSolar MPPT 100/30 with a pair of AGM batteries (around 200Ah total) on the shepherd's hut, and during spring/autumn when the sun isn't exactly blazing, absorption phase sometimes cuts out embarrassingly quickly — we're talking 5-10 minutes some days.

The thing is, Victron's adaptive absorption algorithm calculates absorption time based on how long bulk took. Short bulk = short absorption. Makes sense in theory, but if your panels barely had enough grunt to push through bulk properly, you can end up with a battery that looks full but really isn't.

A few things worth checking if you're seeing the same:

• What voltage are you actually hitting at the end of bulk? If you're not quite reaching absorption voltage before the transition, something's off
• Are your absorption/float voltages set correctly for your specific AGM? Generic presets in Victron aren't always spot-on — worth checking your battery manufacturer's spec sheet
• Panel sizing vs battery capacity — 160W into 136Ah is a reasonable ratio, but on a dull UK day you're not getting 160W

I ended up manually setting a minimum absorption time of around 2 hours in VictronConnect, which made a noticeable difference to how the batteries were actually holding charge.

Anyone else found the adaptive algorithm a bit too clever for its own good on smaller systems? Curious whether tweaking to a fixed absorption time is the better approach for AGMs generally.

@24VGeek classic sign your batteries are already pretty full when solar kicks in — if you're only drawing light loads overnight, they barely discharged, so absorption is genuinely just a few minutes because there's nothing left to top up! 🔋

Worth checking your Victron Connect app history — if your State of Charge is already 90%+ at sunrise, absorption will always be short. Not a fault, just physics being smug.

That said, double-check your absorption voltage is set correctly for AGM (typically 14.4–14.7V for 12V systems) — a Victron defaulting to flooded settings will behave oddly. Also peek at your tail current setting; if it's too high, the controller exits absorption prematurely thinking the battery's full when it isn't.

My shepherds hut setup did exactly this until I tweaked the tail current down to around 2%.

@24VGeek worth checking your absorption voltage setpoint too — if it's set slightly low for your AGM chemistry, the batteries hit target voltage quickly even when they're not truly full, and the controller just... moves on.

AGMs are notoriously fussy. I've seen people running 14.1V absorption when the battery manufacturer specifies 14.4V, and the MPPT declares victory in minutes because it reached a voltage target, just not the right one.

Pull up your battery's datasheet and cross-reference with what VictronConnect is actually configured to. Also check your absorption time algorithm — Victron uses an adaptive system that shortens absorption based on previous charge history, which sounds clever until your batteries genuinely need a proper top-up after a cloudy week.

Not saying your batteries are knackered, but short absorption consistently is worth investigating before assuming everything's fine.

@LiFePO4Nerd has a point on voltage, but also check your tail current setting — Victron lets you terminate absorption early once charge current drops below a configurable threshold, and on a nearly-full AGM that can happen embarrassingly fast.

Mine did exactly this in the motorhome; thought the batteries were dodgy, turned out the tail current was set too generously and it was just... done. Legitimately done.

Also worth logging via VictronConnect over a few days — the history tab will show absorption time trends and you can spot if it's consistently short or just occasional, which tells you a completely different story about what's actually going on.

@FormerCop nailed the tail current point, so I'll add the practical bit nobody's mentioned: check your battery temperature. AGMs have a higher internal resistance when cold, so on a chilly morning the controller hits absorption voltage faster because the battery appears fuller than it actually is. If you haven't got a VE.Smart temperature sensor feeding data to your SmartSolar, you're flying blind on temperature compensation.

Also — what's your absorption voltage set to? Factory AGM presets on Victron are often 14.4V, but many AGMs (particularly cheaper ones) want 14.7V. Pull your battery datasheet and cross-reference.

Run the VictronConnect history graphs and check your daily absorbed Ah — if it's consistently tiny, either your batteries are genuinely full (good problem) or something's throttling absorption prematurely (bad problem). Easy to distinguish once you actually look at the data.