Fitted a 40A DC-DC charger last week and my leisure battery is barely hitting 80% — what am I missing?

Finally got round to installing a Victron Orion-Tr Smart 12/12-30A (yes I know, slightly undersized but it's what I had spare) in my Transit-based van build. Split charge relay is gone, wired it properly into the starter battery positive and chassis earth, and it's all talking nicely to the Victron app via Bluetooth. On paper everything looks fine.

The problem is my 200Ah LiFePO4 (Fogstar Drift) is barely getting above 79-80% after a full day's driving — roughly 4-5 hours on the motorway. The Orion is showing absorption voltage of 14.2V and the battery's BMS isn't cutting anything out early. I'd expect to be close to full given that amount of drive time. The van's alternator is a standard 150A unit so it shouldn't be the limiting factor.

I've checked my cable runs and I'm using 16mm² twin cable, about 2.5 metres total length, so voltage drop shouldn't be catastrophic. One thing I haven't done yet is properly verify the alternator voltage under load at the Orion's input terminals — could a smart alternator be throttling output and starving the charger? The Transit is a 2019 plate so I believe it does have a smart alternator. Would that explain it, or am I barking up the wrong tree?

FrostyTinker | 847 posts | ⚡ Solar & DC enthusiast

@Paddy_2634 Worth double-checking your Bluetooth absorption voltage setting in the Victron Connect app — it needs to match your leisure battery chemistry exactly. Lots of people leave it on the default and wonder why charging stalls early.

Also, what's your typical drive length? The Orion has a fairly lengthy bulk phase, and if you're doing mostly short runs it might genuinely never reach absorption before the engine cuts.

One more thing — have you set the engine detection threshold correctly? If it's triggering shutdown too eagerly based on alternator voltage dip, you're losing charge time unnecessarily. Check the "input voltage lockout" setting.

What battery are you running — AGM, lithium, or wet lead-acid? That'll change the advice considerably. 🔧

@Paddy_2634 check your absorption voltage setting in the Orion's config — if it's set to the default 14.4V but your leisure battery (what chemistry?) needs 14.6V or higher, you'll plateau early and never fully saturate. Also, what's your actual alternator output voltage under load? Many modern Transit alternators are smart/variable-charge units that drop to 12.8–13.2V at cruise specifically to reduce fuel consumption. The Orion needs a meaningful input differential to operate efficiently. If input is sitting at 13.1V and your absorption target is 14.4V, the converter is working hard but runtime may simply be insufficient. Log the VE.Direct data — the Victron Connect app will show you exactly how long it's spending in bulk vs absorption. If it's cutting to float after 20 minutes, that's your culprit.

LazyRanger | 312 posts | 🔋 Van hermit

Also worth checking whether the Orion is actually seeing enough input voltage from the alternator — my Transit dropped to 13.8V under load and the charger basically sulked the whole journey like a teenager. Stick a multimeter on the input terminals whilst driving and see what you're actually feeding it. Also, 30A into whatever leisure bank you've got might just be genuinely slow — my Fogstar 100Ah took a solid 4-hour motorway run before it stopped being dramatic about bulk charge.

Chunk66 | 1,204 posts | 🔧 Sparks & Solar

One thing nobody's mentioned yet — have you checked your alternator output voltage under load? Some modern Fords (Transit included) run smart alternators that drop voltage significantly once the ECU decides the battery's "charged enough." The Orion-Tr Smart has a minimum input threshold, and if your alternator is sagging to 12.8-13V under load, the charger may be throttling back massively or cutting out intermittently.

Worth sticking a multimeter on the input terminals while driving and watching what actually happens. If it's a smart alternator issue, you might need to enable the Orion's engine detection feature properly, or look at triggering it via the ignition line rather than voltage sensing alone. Have a dig through VictronConnect and check the charger history — it'll show you if it's been hitting any input voltage alarms.

WhatsAFuse | 847 posts | ⚡ Van convert

What battery chemistry are you running on the leisure side? If it's LiFePO4 and you haven't told the Orion that, it'll be using a profile designed for AGM/gel — absorption voltage will be too low and the charge algorithm won't push it properly to full.

Also, the Orion-Tr Smart has a temperature compensation feature that can actually reduce charge voltage if it thinks conditions warrant it. Worth checking whether that's throwing things off.

Finally — 30A into what capacity bank? If you're running anything over 100Ah, the maths on charge time might just mean you're not driving long enough to complete a full cycle. The Orion won't lie to you, the VictronConnect app will show you exactly which stage it's sitting in and for how long.

CopperGaffer | 2,156 posts | 🔌 12V & beyond

@Paddy_2634 Worth double-checking your Orion's absorption and float voltages in the Victron Connect app — they sometimes ship with profiles that don't quite suit your specific battery. Also, the 30A unit on a Transit will likely be throttling back due to thermal protection if it's tucked somewhere without decent airflow. Mine ran warm just sitting on a bulkhead shelf. Give it a bit of breathing room and check the app's history tab to see if it's actually delivering consistent current throughout the charge cycle rather than dropping off early.

JaneReid68 | 847 posts | ☀️ Solar & Leisure Electrics

@Paddy_2634 something worth adding to what the others have said — have you confirmed your leisure battery's actual capacity and chemistry? The Orion needs to be configured specifically for your battery type (AGM, gel, lithium etc.). A lot of people set it up and leave the defaults, which can be miles off for certain batteries.

Also, 30A into whatever size bank you've got might simply take longer than you're expecting. If you're only doing short runs, the Orion may never even finish the absorption phase before the engine's off again. What sort of driving are you doing between charges? Worth checking the Orion's Bluetooth history to see how far through the charge cycle it's actually getting each time.