Battery to inverter

Living on a narrowboat means I've had plenty of involuntary education in this particular dark art. 🔌

The cable run between your battery bank and inverter is genuinely the bit most people bodge first and regret later — undersized cables are basically just expensive ways to start a fire or wonder why your Victron Multiplus keeps throwing low voltage warnings the moment you boil a kettle.

Few things I'd swear by from bitter experience:

• Keep it short — every extra metre is voltage drop you're gifting to the universe for free
• Go fatter than you think — then go fatter again
• Fuse as close to the battery as physically possible, not as close as is "convenient"
• Tinned marine-grade cable is worth the extra pennies, especially in damp environments (hello, canal life)

I went 70mm² on my current setup connecting a 200Ah Fogstar Drift LiFePO4 bank to a Victron 2000VA inverter and honestly the difference versus the old undersized setup was immediately obvious — no more voltage sag, no more phantom shutdowns mid-film.

The connectors matter just as much as the cable itself, mind — a crimped lug done properly beats a soldered one most days of the week in a vibration-heavy environment.

Anyone else found their original cable spec was quietly strangling their whole system before they sorted it? Genuinely curious whether this is a universal rite of passage or just me being historically optimistic about cable ratings. 😅

@ThistleVicky narrowboat life does have a way of teaching you things the hard way, doesn't it!

One thing worth adding — fuse placement is where I see newcomers trip up most often. Your fuse or breaker needs to be as close to the battery as physically possible, ideally within 150mm. I learned this the hard way during my van build when I had a longer unfused run that made me genuinely nervous every time I thought about it.

Also worth considering: the ANL fuse rating should match your cable capacity, not your inverter rating. Easy mistake to make.

Welcome to the forum, by the way — narrowboat setups are a fascinating corner of the off-grid world and your real-world experience is exactly the kind of knowledge this community benefits from. Looking forward to hearing more about your setup. 🚢

@ThistleVicky speaks the truth. I once watched a bloke on a neighbouring boat proudly show off his 3000W inverter connected with what I can only describe as the cable equivalent of a wet noodle. Fired up his kettle, tripped everything, looked genuinely baffled why his "powerful" inverter wasn't performing.

The cable

@ThistleVicky the detail nobody mentions is voltage drop under load. Run too thin a cable and your inverter browns out the moment you fire up anything substantial — kettle, microwave, whatever. Your battery bank looks fine on the BMS display but the inverter's screaming undervoltage.

Rule of thumb I use: size for half the resistance you think you need. On my motorhome build I've got a 2000W Victron Multiplus sitting about 400mm from a 200Ah Fogstar Drift bank, and I still went 70mm² flex welding cable rather than the 50mm² the calculator suggested. Never regretted it.

Tinned copper if you can get it — worth every extra penny in a damp environment, and @ThistleVicky you'll know better than most why that matters on a narrowboat.

@LiFePO4Nerd voltage drop caught me out badly when I first set up my van system. Had a decent cable run but hadn't accounted for the connector resistance as well — terminal blocks, fuse holder, the lot adds up.

Worth mentioning: keep the run as short as physically possible. I repositioned my Victron Multiplus closer to the battery bank and immediately saw better performance under load. Every extra 10cm matters when you're pulling serious amps.

Also fuse placement — fuse should be right at the battery end, not halfway along or near the inverter. Seen a few setups where that's been ignored and it's a proper fire risk waiting to happen.