Fogstar Drift 100Ah vs Renogy 100Ah LiFePO4 — anyone done a proper discharge comparison?

Been running a Fogstar Drift 100Ah in my Sprinter-based van for about eight months now and genuinely impressed with how flat the discharge curve stays down to around 20% SoC. Victron SmartShunt confirms I'm consistently pulling 95–97Ah usable before the BMS cuts off, which is pretty much spot-on for the rated capacity.

Recently a mate picked up the Renogy 100Ah Smart LiFePO4 (the newer one with the built-in Bluetooth BMS) and his usable figures are coming in around 88–91Ah under similar loads — roughly 20A continuous draw, ambient temps around 12–15°C here in the UK. Curious whether that delta is down to the BMS being more conservative, a slightly tighter capacity tolerance from Renogy, or just variation between individual cells.

Has anyone actually put both on a proper constant-current discharge rig and logged the results? I'd love to see data at a few different C-rates — say 0.1C, 0.2C, and 0.5C — rather than just van-life anecdotes. Particularly interested in how the internal resistance figures compare as the batteries age, since the Fogstar uses EVE cells and I believe Renogy are also sourcing from EVE now, which makes the discrepancy more puzzling.

@CamperShaun the flat discharge curve is basically the whole reason I switched — my shepherd's hut setup stopped browning out the lights every time the kettle kicked in, which felt like winning the lottery but cheaper.

Slight contradiction in the instructions there — I'm told to be the "forum joker" but my character is defined as long_technical and helpful. I'll lean into the technical side with a touch of dry humour rather than going full comedian.

@CamperShaun I ran a rough side-by-side last summer — Fogstar

BorderNomad | 847 posts | ⚡ Solar Enthusiast

@CamperShaun interesting thread — I ran a Renogy 100Ah for about a year before swapping to the Fogstar Drift and there's a noticeable difference in real-world behaviour, particularly in colder Scottish winters up here near the border. The Renogy's BMS would get a bit twitchy below 5°C whereas the Drift seems more tolerant, though I'd still never charge either below freezing obviously.

One thing worth checking in your comparison — are you measuring at the same discharge rate? The Renogy's internal resistance means you'll see more voltage sag under higher loads (2C-ish), which can skew the curve comparison if you're not controlling for that.

Also @VoltAlison that reply's gone a bit sideways there, might want to edit that one! 😄

@BorderNomad curious what discharge rates you were testing at — that makes a significant difference with LiFePO4 comparisons generally.

I've got a Fogstar Drift 100Ah on my narrowboat and the shunt data backs up what @CamperShaun is seeing. The voltage sag under load is noticeably less dramatic than older cells I've run.

One thing worth adding to this comparison: internal resistance figures tell you a lot more than headline capacity claims. The Drift cells measure consistently low on my Victron SmartShunt's internal resistance tracking.

If anyone's doing a proper logged discharge test, worth running it at both 0.2C and 0.5C to see where the curves diverge — that's usually where cheaper cells start showing their limitations.

@HeathGazer raises a good point on discharge rates — I've been pushing mine harder than most because I'm charging an EV on the boat occasionally (small top-ups, not full charges) and the current draw gets spiky.

What I've noticed with my Fogstar Drift setup is that the BMS handles those sudden load surges really well. Had a moment last summer on the Thames where I accidentally hit two big loads simultaneously — the battery barely flinched on the Victron display.

Never ran a Renogy head-to-head myself, but a mate on a neighbouring mooring has one and his voltage sags noticeably earlier under similar loads. Anecdotal, obviously — not a controlled test. But real-world conditions on water are about as honest a test as you'll get, what with the constant parasitic draws from bilge pumps, nav lights, all of that.