Swapped out my 100Ah AGM for a 100Ah Fogstar Drift LiFePO4 — worth it?

Finally pulled the trigger last month after years of running a Varta AGM on my campervan conversion. The Fogstar Drift 100Ah came in around £280 which felt reasonable compared to some of the Victron lithium options. Install was straightforward, just had to reprogram my Victron SmartSolar MPPT to the lithium profile and adjust absorption/float voltages.

The difference in usable capacity is pretty noticeable. With the AGM I was nervous taking it below 50%, so realistically had about 50Ah to play with. Now I'm comfortably running the van down to 20% without any stress, which in practice feels like a completely different setup even though it's the same physical battery size. Running a 40L Waeco fridge, some LED lighting, and charging phones/laptops off a 200W Renogy panel.

One thing I wasn't expecting — the Fogstar gets surprisingly warm during bulk charging on sunny days. Nothing alarming, but more than I anticipated. Anyone else noticed this with the Drift specifically, or is that just lithium in general? Also curious whether anyone's run one through a proper UK winter yet, since I know LiFePO4 can have charging issues in low temps.

@RobBennett93 Really interested in this — I've been going back and forth on the exact same decision for my van build. Did you need to change anything on the charging side, or did your existing setup handle the LiFePO4 charge profile okay? I'm running a Renogy DC-DC charger at the moment so think I'd be covered, but my solar controller is a basic PWM unit which I've heard can be a bit iffy with lithium. Also curious whether the 100Ah usable capacity actually feels like a proper upgrade in day-to-day use — on paper going from ~50Ah usable on AGM to ~90Ah on LiFePO4 should be transformative, but wondering if you noticed it practically, especially during overcast days when you're not getting much solar input.

@RobBennett93 Worth flagging that the usable capacity difference is the real story here — your 100Ah AGM was realistically giving you ~50Ah before you risked damaging it, whereas the Fogstar Drift delivers ~95Ah all day. Effectively you've nearly doubled your usable storage without adding a second battery.

One practical point from my shepherd's hut build: make sure your charger's charge profile is actually set to LiFePO4 (absorption ~14.2–14.6V, no equalisation). Loads of people leave it on AGM profile and either undercharge or stress the BMS. Victron kit handles this cleanly, but worth checking whatever you're running.

The Fogstar Drift's built-in BMS is solid for the price — I've had mine in continuous use for 14 months without complaint.

@BatteryBarry makes a good point on usable capacity — that's exactly what sold me when I was speccing out my garden office setup.

One thing I'd add: weight saving is massive if you're building a van conversion. LiFePO4 is roughly half the weight of AGM at the same Ah rating. Matters a lot for payload and handling.

Also worth checking your charger profile — my old B2B charger needed a firmware update to handle lithium properly. Caught it before any damage but easily missed.

£280 for the Fogstar Drift is solid value. I've seen people pay that for budget AGMs that won't last five years. The cycle life difference alone justifies it long term.

@BatteryBarry and @MeganFox have already nailed the usable capacity point so I won't rehash that, but one thing I'd add from my own Drift experience — the weight saving is genuinely noticeable in a van conversion. My 100Ah AGM was around 28kg, the Drift is closer to 13kg. When you're trying to keep payload sensible that actually matters.

Also worth mentioning @RobBennett93 — check your alternator charging setup. LiFePO4 will happily draw much harder from your alternator than an AGM would, so if you're doing longish drives it's worth considering a DC-DC charger (B2B) rather than just charging direct. Protects your alternator and conditions the charge properly. Sterling and Victron both do decent units at various price points. Might be something to factor in if you haven't already sorted that side of things.

Great shout on the Fogstar Drift, @RobBennett93 — solid choice at that price point.

One thing nobody's mentioned yet: check your charging sources are actually LiFePO4-compatible. Your van's alternator charging via a B2B (DC-DC) charger is fine, but if you've got an older split-charge relay setup, you could end up with the BMS cutting out mid-drive as the battery hits full charge — not ideal and potentially confusing to diagnose.

Also worth checking your solar controller has a LiFePO4 profile if you're running panels. Most decent MPPT units do, but older PWM controllers can be a bit hit and miss. Small tweaks, but they make a real difference to longevity. 🔋

@RobBennett93 The bit nobody mentions until it's too late — your charging profile needs updating too. Most vehicle alternators and older B2B chargers are tuned for AGM absorption voltages. Running that into a LiFePO4 without a proper DC-DC charger in between is asking for grief long-term, sometimes shorter-term.

I learned this the hard way on my shepherd's hut build before I eventually got a Victron Orion-Tr Smart sorted. Night and day difference, and the battery's been spot-on for two seasons now.

The Fogstar Drift is genuinely solid kit for the money — just don't assume the rest of your system speaks the same language as it does straight away.

Great write-up @RobBennett93! One thing worth flagging that I don't think's been touched on yet — LiFePO4 doesn't like being charged in cold temperatures. Below around 5°C you risk damaging the cells, so if you're doing winter trips and the van's been sitting overnight, let it warm up a bit before your solar or alternator starts pushing charge in. Some of the pricier batteries have built-in low-temp cutoffs but I'm not sure the Drift does at that price point — worth double-checking with Fogstar directly. Might be something to keep an eye on heading into autumn.

Really useful thread, just saved it for when I make the jump myself.

Quick question that's been nagging me — does the Fogstar Drift have its own built-in BMS, or do you need to add one separately? I've seen some cheaper LiFePO4 batteries where the BMS is almost an afterthought and causes grief down the line.

Also @WattBarry raises a good point about charging profiles — does anyone know if a basic Victron IP22 handles the LiFePO4 profile out of the box, or does it need reconfiguring through the app first?

Great move @RobBennett93, the Drift is solid value for money. One thing I'd add that nobody's picked up on yet — keep an eye on your low voltage cutoff settings. LiFePO4 has a much flatter discharge curve than your old AGM, so your existing low-voltage alarm will likely trigger far later than you'd expect, almost at the cliff edge of the battery's usable capacity. Worth setting any inverter or BMS cutoff around 12.0V (resting) to give yourself a proper safety margin rather than relying on gut feel like you could with lead acid.