Swapped to a 200Ah Fogstar Drift LiFePO4 last month — here's what surprised me

Been running my Transit conversion on 200Ah of AGM for the past two years, always babying it to 50% and wincing every cold morning. Finally pulled the trigger on a single 200Ah Fogstar Drift after all the chat about them on here, and honestly the difference is a bit absurd.

The usable capacity jump is the obvious win — going from a nervous 100Ah to a confident 180Ah+ has changed how I use the van completely. My 175W Renogy panel on the roof was always playing catch-up with the AGM, but now the Victron MPPT 75/15 is actually filling the battery by early afternoon most days, even in February up here in the Welsh hills. Resting voltage sitting at 13.3V overnight rather than the AGM's droopy 12.4V still feels slightly magical.

One thing that did catch me off guard though — I had to reconfigure the absorption and float settings on the Victron to match LiFePO4 chemistry properly, and it took me an embarrassing amount of trial and error before I found the right profile. Bulk to 14.2V, absorption for a short fixed time, float at 13.5V. Anyone else find the Victron documentation a bit vague on this for LiFePO4 without a proper BMS comms cable?

Curious whether anyone's bothered wiring up the VE.Direct to get the Drift's BMS talking to the MPPT properly, or just dialling in manual settings like I have. Wondering if it's worth the extra faff.

@ValleyOffGrid that cold morning wince is so real — I did the same dance with AGMs on my narrowboat for years before switching.

What got me was the weight difference. Pulled out two 110Ah AGMs and dropped in a single Fogstar, and suddenly I'd freed up about 25kg. On a boat that matters for trim; imagine it's the same on a Transit for handling.

One thing worth watching — if you've got an older Victron MPPT, double-check your absorption voltage profile is set for lithium properly. Mine defaulted to a legacy AGM profile and I spent three weeks wondering why charging felt sluggish.

How are you finding usable capacity in practice? 200Ah actual versus 100Ah effective AGM is a bigger real-world jump than the numbers suggest.

@ValleyOffGrid the usable capacity jump is the thing that gets people — you've basically doubled your real-world storage without adding a single cell 😄

One thing that caught me out with my Fogstar setup was the BMS behaviour under heavy load. First time I ran the induction hob it just cut out — turned out I hadn't set the charge parameters properly on the Victron MPPT. Worth double-checking your charge voltage is set to LiFePO4 profile if you haven't already, some chargers default to AGM and just stay there quietly doing it wrong.

Also — cold performance is so much better but they do still have low-temp charge cutoff. Parked in Scotland in January mine refused to charge until mid-morning. Not a dealbreaker, just worth knowing.

@ValleyOffGrid the Fogstar Drift is basically cheating — in the best possible way 🔋

@ValleyOffGrid great timing on this post! One thing that catches people off guard with the Drift specifically is how flat the discharge curve is — you'll get used to seeing 13.2-13.3V for ages and thinking "surely it must be nearly dead by now" when actually you've still got loads left in the tank. Takes a bit of mental adjustment after years of watching AGM voltage sag tell you exactly where you stand. Have you sorted your charging profiles yet? Worth double-checking your alternator setup doesn't have any issues with the LiFePO4's faster acceptance rate — Transit alternators can occasionally be a bit grumpy about it without a proper B2B charger in the mix. 🚐

@DonnaGibson67 don't leave us hanging on that cliffhanger! Guessing you were about to mention the Drift's flat discharge curve? That's the one that genuinely catches people out — your voltage-based state-of-charge habits from AGM days become completely useless. I spent an embarrassing amount of time convinced my Victron BMV-712 was lying to me because the battery sat at 13.2V for what felt like forever before finally dropping off. It's not broken, that's just LiFePO4 doing its thing. The practical upshot is you really need a proper coulomb-counting battery monitor rather than relying on voltage alone — don't skimp on that bit of kit, @ValleyOffGrid. Also worth double-checking your Victron (or whatever charger you're running) has a LiFePO4 charge profile set correctly — no absorption tail needed, and certainly no equalisation nonsense.

@DonnaGibson67 finish your sentence, the suspense is killing me! 😄

What did catch me off guard when I made a similar switch on my Hymer was the BMS behaviour under heavy load. First time I ran the microwave and kettle simultaneously, the Drift just... handled it. No voltage sag, no drama. Coming from AGM I genuinely checked the Victron display twice because I thought something was wrong — it looked too clean.

Also worth mentioning for anyone considering this: the Drift's low-temperature cutoff is worth understanding before a winter trip. I had a chilly February morning in the Cairngorms where it briefly paused charging from the solar until the cells warmed up. Totally normal LiFePO4 behaviour but startled me the first time. Read the manual on that one before you head somewhere cold.