Victron Smart Solar 150/85 Charge Controller not absorbing for programmed duration

Had this exact issue last summer with my cabin setup. The MPPT will cut absorption short if it reckons the battery is already close to full — it's called adaptive absorption and it's on by default.

Basically Victron's algorithm watches how long bulk took. Short bulk = battery wasn't that depleted = shorter absorption. Makes sense in theory but it can feel wrong when you're expecting the full programmed time.

A few things worth checking:

• VictronConnect app → go into the battery settings and check if adaptive absorption is actually enabled (might want to disable it temporarily to test)
• What battery type are you running? If it's lithium you'll want a proper Li profile sorted
• Check your tail current setting — if the current drops below that threshold it'll jump to float early regardless

I switched to Fogstar Drift lithium cells last year and had to completely revisit my absorption settings. The defaults Victron ships with are quite conservative for certain chemistries.

Also worth pulling up the history tab in VictronConnect — it'll show you exactly how long absorption ran each day over the past 30 days. Really useful for spotting patterns.

What batteries are you on and what's your typical daily usage? That'll help narrow it down. Others on here have probably seen the same — @anyone with a 150/85, jump in if you've got thoughts.

Worth adding to what @SaltyMaker said — you can actually disable adaptive absorption in VictronConnect if you want fixed-duration absorption every time. Go into the charger settings and there's a toggle for it.

That said, on my van setup I've left it enabled and honestly it works well once the batteries are properly cycled in. The algorithm learns your battery's behaviour over time.

One thing worth checking though: battery temperature. If you've got a temp sensor fitted, Victron will adjust absorption based on that too. Had mine cutting short on cold mornings in the Fens before I realised the sensor was reading a bit off.

What battery chemistry are you running? LiFePO4 behaves quite differently to AGM with adaptive absorption — might be relevant to your situation.

Before you start fiddling with adaptive absorption settings, worth checking your battery cable voltage drop first — if the controller is seeing a higher voltage at its terminals than the battery's actually getting, it'll think absorption is done when it isn't, and no amount of menu-diving fixes a dodgy connection.

Caught me out on my garden office build; Victron MPPT was cutting absorption 40 minutes early, turned out my negative busbar connection was about as solid as a politician's promise.

Stick a multimeter across the battery terminals during charge and compare it to what VictronConnect is reporting — if there's more than ~0.2V difference you've found your culprit before blaming the software.

Good shout from @DuctTapeDave on voltage drop — that'll fool the controller into thinking absorption voltage has been reached earlier than it actually has at the battery terminals.

Worth being methodical about it:

1. Measure voltage at the controller vs at the battery under load
2. Anything over ~0.2V difference suggests your cabling needs attention

I had this exact problem with my shepherd's hut setup. Turned out my negative busbar connection had a dodgy crimp — controller was seeing full absorption voltage fine, battery terminals told a different story. Sorted the cabling first, then reassessed whether adaptive absorption was actually the culprit.

Fix the fundamentals before changing software behaviour.

@DuctTapeDave and @CurrentAffairs make a good point on voltage drop — caught me out on my shepherd's hut build. Spent ages messing with absorption settings before I realised my cable run was borderline undersized.

Worth actually logging the data in VictronConnect rather than guessing — you can see exactly where voltage is landing at the battery terminals vs what the MPPT thinks it's seeing. Made it obvious in my case.

Also check your battery temp sensor if you've got one fitted. Mine was reading a bit high one afternoon, so the controller was backing off absorption voltage thinking it needed to protect the cells. Turned out the sensor had shifted position and was sitting in direct sun 🤦

Sort the fundamentals first, then look at adaptive absorption settings.