Swapped out my split charge relay for a B2B charger — worth every penny or overkill?

So I've been running a 100Ah AGM leisure battery in my Transit-based camper for a couple of years, fed by a basic split charge relay off the alternator. It's always been... fine, I suppose, but I noticed the battery rarely seemed to get above about 80% charge even after a decent motorway run. Did a bit of reading and kept seeing people bang on about DC-DC B2B chargers, so I took the plunge and fitted a Victron Orion-Tr Smart 30A a few weeks back.

The difference has been pretty noticeable if I'm honest. The battery is actually hitting full charge now after a couple of hours of driving, and I can monitor it properly through the Victron app which I wasn't expecting to enjoy as much as I do. Fitted it under the passenger seat with a 30A inline fuse close to the starter battery — fairly straightforward job for an afternoon.

What I'm wondering is whether anyone else has made the same swap and whether 30A was the right call, or if I should have gone bigger. My solar (a single 175W panel on the roof) handles most of my static needs, but I rely on driving charge when I'm moving between sites in winter when the sun disappears for days at a time.

Anyone running the 18A version instead and finding it sufficient, or is that going to leave me frustrated on shorter runs?

PYW_VanLife | Posts: 847 | Location: South Wales

@OakTel I made exactly the same swap about 18 months ago and honestly the difference was immediately noticeable. The relay was only ever getting my AGM to around 70-75% because of the voltage drop issue — the B2B actually pushes a proper three-stage charge profile regardless of what the alternator's doing.

Worth noting particularly with modern Euro 6 engines — the smart alternator management systems mean a relay is practically useless half the time anyway, since the alternator deliberately drops voltage to save fuel.

The upfront cost stings a bit, but if you're preserving battery life and actually getting full capacity back each day, it pays for itself fairly quickly. What size B2B did you go for? I'm running a Victron Orion 30A and it's been faultless.

YEL_Marine | Posts: 312 | Location: Norfolk Broads

The thing people don't mention enough about B2B chargers is the benefit to your alternator's health, not just the battery. A relay essentially dumps your depleted leisure battery straight across the alternator circuit, which can stress modern smart alternators something rotten — especially on Euro 6 Transits where the ECU is managing charge voltage dynamically.

With a B2B you're drawing a controlled, consistent current regardless of battery state. Your alternator will thank you long-term.

@OakTel what size B2B did you go for? A 30A unit on a 100Ah AGM should see you reasonably well charged after a decent motorway run, though if you're moving to lithium down the line you'll want to check it supports that profile properly.

Dave1984 | Posts: 1,203 | Location: Peak District

Worth flagging something @OakTel — modern Transits with smart alternators are actually designed to vary voltage, so a basic split charge relay is genuinely problematic rather than just suboptimal. The alternator will often drop output when the ECU decides it doesn't need to charge, and your relay sees that as "engine off" and disconnects. A B2B charger handles that variable voltage properly and just gets on with the job regardless.

I made the switch two years ago on my Sprinter and the difference in how fully my AGMs actually charge was noticeable within the first week. Battery lasting noticeably longer between hook-ups on site.

What B2B unit are you looking at? The Victron Orion range is popular on here, though Sterling and Renogy both offer decent alternatives if budget's a consideration.

FogstarFan | Posts: 1,203 | Location: Array

Split charge relay is basically just "electricity if vibes align" whereas a B2B actually manages the charge profile properly — your AGM will thank you for not being perpetually half-cooked at 13.8V. Running a Victron Orion-Tr Smart in the motorhome and it's transformative; isolates intelligently when the engine stops, plays nicely with modern smart alternators that would otherwise throw a fit at a dumb relay hammering them with load. If you ever upgrade to lithium (and you will, we all do eventually), a B2B becomes non-negotiable rather than just sensible. Fogstar Drift 100Ah + Orion combo is practically the forum starter pack at this point.

StevePrice89 | Posts: 847 | Location: Array

Made the same swap on my shepherd's hut boat build last year — Victron Orion-Tr Smart 30A. Night and day difference.

One thing nobody's touched on yet: the Bluetooth monitoring is genuinely useful. You can see exactly what's going into your leisure battery in real time, rather than just hoping the relay clicked properly.

Also worth noting — if you ever upgrade to lithium down the line (Fogstar Drift is what I went with), the B2B handles the charge profile correctly. A basic relay definitely won't.

@OakTel what's your solar situation? If you've got panels too, the Orion pairs really nicely alongside a proper MPPT. My setup runs both simultaneously and the battery fills up surprisingly fast even in rubbish UK weather.

ExBrickie | Posts: 634 | Location: Array

@StevePrice89 curious which Victron Orion you went with — the isolated or non-isolated? That choice trips a lot of people up.

On a Transit specifically, the non-isolated can work but if you've got any shared earth paths between chassis and leisure battery setup, isolated is the safer bet. Learnt that the hard way on my boat before I sorted the earthing properly.

One thing nobody's mentioned — check your alternator rating before you spec the B2B. A 30A Orion pulling constantly on a smaller alternator in stop-start town driving isn't ideal. The Victron handles it better than some cheaper units, but it's still worth considering the 18A version depending on your use case.

The upgrade is worth it. Just don't sleepwalk into it assuming any B2B is automatically the right B2B.

MXM_OffGrid | Posts: 2,156 | Location: Lincolnshire

@ExBrickie — good question on the isolated vs non-isolated front. For a Transit specifically, I'd lean toward isolated every time. Ford's smart alternator setup can behave oddly when the two battery negatives share a common ground, and you can end up with some weird voltage readings confusing the BMS or charge controller. The non-isolated units are cheaper and perfectly fine in simpler, older vehicles, but modern Euro 6 vans with variable voltage alternators really benefit from proper isolation. @OakTel what year is your Transit? That'd help narrow down which route makes most sense for your setup.

LDVWanderer | Posts: 312 | Location: Array

Running a B2B on my boat and honestly can't imagine going back to a relay. The big thing nobody mentions enough — modern alternators with smart charging (variable voltage) will actually confuse a relay setup and you end up barely charging your leisure bank at all. The B2B basically tricks the alternator into thinking it's seeing a proper load consistently.

Worth checking what alternator your Transit has before buying — some of the newer Euro 6 ones throttle output aggressively and you might want to size up to a 30A unit rather than the standard 18A.