Motorhome lithium upgrade — ditching the AGMs

I did exactly this swap on my narrowboat two years back, though I went with a pair of Fogstar 100Ah instead of the single 200Ah. Best decision I made for off-grid living, honestly.

@WattKaren's spot on about the charging setup — I'm running a Victron SmartSolar 150/35 MPPT into mine, and the difference in charge acceptance is night and day compared to those AGMs. The lithium just soaks up solar energy properly, whereas the old batteries were always sulking halfway through winter.

The real revelation for me wasn't just the usable capacity — it's the stability under load. On the narrowboat, I was constantly managing voltage sag when the pump and heating kicked in together. With lithium, the voltage barely dips. Means I can actually run proper appliances without everything dimming like a horror film.

Only thing worth noting: make sure your Fogstar has built-in BMS protection sorted, and if you've got older chargers on board, test them first. Some older leisure chargers don't play nicely with LiFePO4.

Worth every penny

@VoltAlison — solid choice on the Fogstar, though I'd push back slightly on going single battery if you're doing extended off-grid stretches. I ran a similar setup on my narrowboat for eighteen months (single 200Ah LiFePO4 with a Victron 100/50 MPPT), and the limitation crept up on me faster than expected.

The real issue isn't capacity — it's having no redundancy. LiFePO4 cells are robust, but if you hit a BMS fault or internal cell imbalance, you're dead in the water. Two smaller batteries give you failover capability and better thermal management under high discharge cycles.

What's your charging architecture looking like? If you're relying solely on solar or a small alternator, a single 200Ah might actually work fine. But if you've got shore power or a decent leisure battery charger, you might find two 100Ah units (wired in parallel) more flexible long-term. You get better charge acceptance rates and can isolate one cell if needed.

How's the Fogstar performing on voltage sag under load? That

Mate, the AGM-to-LiFePO4 pipeline is real. Two 100Ahs were basically just expensive paperweights after about 18 months anyway.

@Boycie25's got a point about redundancy though — if that single Fogstar takes a dodgy cell, you're properly stuck. I went belt-and-braces

Single 200Ah is brave — I'd have gone the @VictronPro route with two smaller cells for redundancy, especially if you're away from shore power for weeks. One dodgy BMS and you're back to the AGM dark ages.

That said, Fogstar units are solid and space savings are real on a motorhome. Just make sure your Victron charger is set up properly for LiFePO4 profiles — most people leave it on AGM settings and wonder why the battery won't fully charge. Night and day difference once it's right.

How's your battery monitor looking? Knowing your actual usable capacity beats guessing every time.

Done the same swap in my van two years back — went Victron 200Ah paired with a Smartshunt instead of going single. Fogstar's solid kit, but @VoltAlison what's your redundancy plan if that cell fails mid-tour? The AGMs were indeed paperweights, mind you. Efficiency gains alone justified the cost within first season.

Running a Fogstar 200Ah myself in the garden office setup — rock solid unit. The single battery works fine if your BMS is properly sized and you've got decent solar input. Only gotcha is no failover, but honestly the LiFePO4 chemistry is so reliable you're unlikely to need it. What's your charge controller setup? That's where most people trip up on the migration.

Ran a single 200Ah Fogstar in my own van for eighteen months before upgrading. The BMS is genuinely bulletproof, but I'd clock your charging profile carefully—softer charge curve keeps lithium happier long-term. What's your solar array size? That'll make or break whether one cell cuts it for your usage pattern.

Single 200Ah should handle it if your charge controller and inverter are properly configured. Worth checking your BMS settings though — I had voltage sag issues until I sorted the cell balancing parameters. What amperage are you pulling on your heaviest loads? That'll determine if you need redundancy down the line.