Anyone else had grief with a Victron MultiPlus 24/2000 dropping to float too early on a cold morning?

Been scratching my head with this one for a few weeks now. Running a 24V system with 200Ah of AGM batteries in my shepherd's hut, and the MultiPlus seems to be calling absorption done way too quickly on cold mornings — we're talking sub-5°C out here at the moment. It hits absorption for maybe 40 minutes then drops to float at around 26.8V, and the batteries just don't feel properly topped up by end of day.

I've got a BMV-712 on there and it's showing the batteries rarely get above 85% SOC before the MultiPlus decides it's done. Charging current is still sitting at 8–10A when it switches over, which doesn't feel right to me. I know AGMs want a proper absorption phase, and I've read that cold temps mean you really need to let them sit up there longer before dropping off.

I haven't got a temperature sensor fitted yet — is that the obvious fix here? I know Victron do the VE.Bus Smart Dongle and there's also the dedicated battery temp sensor that wires straight to the MultiPlus. Just wondering whether that alone would sort the early float issue, or whether I need to go digging in VEConfigure and tweak the adaptive absorption settings manually as well.

Has anyone dealt with this specific combo — MultiPlus and AGMs in cold conditions? Would love to know what settings people have landed on.

@Lefty91 classic cold battery issue this. AGM internal resistance rises significantly below about 10°C, so the charge current drops off faster than it should during absorption — the MultiPlus sees low current and assumes the battery is full when it absolutely isn't.

Two things worth checking in VE.Configure:

1. Adaptive absorption — if enabled, it's calculating absorption time based on bulk duration, which gets skewed when bulk ran short due to cold sluggishness
2. Tail current threshold — default is often set too high; dropping it to 1–2% of capacity gives colder batteries more time to properly accept charge

Honestly the proper fix is a Victron Smart Battery Sense or a temperature-compensated charge profile. AGMs want roughly -4mV per cell per °C compensation, so 24V (12 cells) means the voltage target needs lifting noticeably on a cold morning in a shepherd's hut with no heating.

FrankPalmer | Posts: 847 | Location: Derbyshire

@Lefty91 Worth checking your absorption time settings in VEConfigure - by default the MultiPlus uses adaptive absorption, which calculates duration based on the previous discharge. If the batteries didn't discharge deeply (perhaps overnight wasn't that cold yet), it'll shorten absorption accordingly. That combined with what @LDVConvert mentioned about rising internal resistance can fool the charger into thinking it's done.

Try switching to fixed absorption time temporarily - I'd suggest 3-4 hours for 200Ah AGMs - and see if your resting voltage holds better afterwards. Also, have you got a battery temperature sensor fitted? The MultiPlus supports one and it'll automatically compensate the charge voltage downward in summer and upward when it's cold. Genuinely transforms cold-weather performance. Should be under a tenner for the Victron sensor cable.

Got a temp sensor on those AGMs yet? Victron's battery temperature sensor is about £15 and tells the MultiPlus to compensate automatically — without it, your charger's essentially flying blind in a woolly jumper on a cold morning.

KenMurray | Posts: 312 | Location: North Yorkshire

@Lefty91 One thing nobody's mentioned yet — have you checked your battery capacity setting in VEConfigure? If it's set lower than your actual 200Ah, the MultiPlus will calculate absorption time from that figure and cut short accordingly. Easy to overlook if the unit came second-hand with someone else's config still loaded.

Also worth looking at your bulk voltage — cold AGMs need it nudged up slightly to actually reach the absorption threshold properly, otherwise you're starting the absorption timer from a point where the batteries aren't remotely full. Combined with the shortened absorption time, you end up with chronically undercharged batteries going into float. The temp sensor @PartnerCamper mentions handles the voltage compensation side of that automatically, mind.

OddJobBob17 | Posts: 1,203 | Location: Shropshire

@Lefty91 Worth adding to what @PartnerCamper said about the temp sensor — AGMs in cold conditions can show a surface charge fairly quickly, which fools the voltage-based absorption timer into thinking they're fuller than they actually are. The MultiPlus sees the voltage tick up and thinks "job done."

Have a look at your repeated absorption settings too. If the battery hasn't been properly cycled for a while, enabling repeated absorption (I think it's a 7-day default) can help ensure it goes back through a proper bulk/absorption cycle rather than jumping straight to float next time round.

What's your absorption voltage set to? At 24V with AGMs you'd typically want around 28.4–28.8V. If it's on the low side that could be contributing to the premature cutoff, especially when the batteries are cold and internal resistance is higher.