Victron Multiplus keeps dropping to float too early — anyone else had this?

Had this exact issue with mine last winter — turned out the absorption time was set so short it was basically just waving at the batteries as it flew past.

Worth checking a few things in VEConfigure:

• Absorption time — if you're on adaptive absorption, it bases the time on the previous charge cycle, which can snowball into shorter and shorter periods if you've had a few easy days
• Tail current setting — if this is too high, the Multiplus thinks the batteries are full when they're clearly not. I'd dropped mine to 1% of battery capacity and it sorted itself right out
• Battery capacity entered correctly? — mine had a daft figure in there from the original install, basically telling the unit the bank was half what it actually is

I'm running Fogstar Drift lithium here so also had to make sure the charge profile wasn't still set up for lead acid — completely different absorption behaviour and the Multiplus doesn't read minds, unfortunately.

Also worth grabbing VRM or a Cerbo if you haven't already, because watching the charge curve in real time is the only way you'll actually catch what's happening rather than guessing.

Anyone else found adaptive absorption more trouble than it's worth on smaller systems? I've half a mind to just fix the absorption time and be done with it — the "smart" settings occasionally feel like they were written by someone who's never actually lived off-grid.

@AlanJones63 good shout on VEConfigure — worth adding that the repeated absorption setting is often overlooked too. If your Multiplus sees the battery voltage hit absorption target quickly (common with lithium or a partially-discharged AGM), it can interpret that as "job done" and bail early.

Also check your tail current threshold — that's the amperage at which it decides absorption is complete. Factory default can be surprisingly aggressive depending on your battery bank size.

For anyone running Fogstar or similar LiFePO4, make sure your charge profile is actually matched to the BMS specs rather than a generic lithium preset. I spent a frustrating week last autumn chasing ghost issues before realising my tail current was set for a 100Ah bank but I'd upgraded to 200Ah.

Good points from both of you. One thing I'd add — if you're running lithium (Fogstar Drift cells are popular on here), make sure your battery capacity figure in VEConfigure is accurate. The adaptive absorption algorithm calculates dwell time partly from that value, so if it's undersized you'll get premature float transitions regardless of your minimum absorption time setting.

Also worth checking the tail current threshold. Default is often 4% of charge current — on a small bank that can be surprisingly easy to hit even when the cells aren't truly full.

I caught this on my shepherds hut setup last summer. Bumped the capacity figure to match actual usable capacity and the absorption phase immediately behaved more sensibly. @VivaroWanderer's repeated absorption point is genuinely important too if you're seeing it across multiple charge cycles.

@BordersExplorer good point on the lithium side — worth mentioning that if you're on lead acid (AGM especially), temperature compensation matters a lot in winter. Cold batteries need higher absorption voltage or they'll never actually fill properly, so the Multiplus bails out thinking it's done when it really isn't.

Had this exact problem with my backup setup last year — Victron SmartShunt sorted it because the temp sensor feeding into the charge profile meant the Multiplus actually knew what was going on. Before that it was just guessing.

Also double-check your battery capacity setting in VEConfigure is accurate — if it thinks you've got smaller capacity than you do, absorption time calculations go wonky from the start.

@Hamish1975 temperature compensation on AGM is basically doing all the heavy lifting in winter while you're sat there blaming Victron for everything — mine was reading 2°C in the garage and dropping to float so fast the batteries barely noticed they'd been charged.