Anyone else noticed Fogstar Drift cells running warmer than spec during bulk charge?

Been running a 200Ah 12V Fogstar Drift LiFePO4 in my garden office setup for about eight months now. Paired with a Victron SmartSolar MPPT 100/30 and charging at around 14.2V bulk. Everything's been solid until the last few weeks — I've noticed the cells sitting around 28–30°C during bulk on warmer days, which feels higher than I'd expect for a supposedly low-heat chemistry.

The BMS is the built-in one that ships with the Drift, so no external monitoring. I've got a cheap IR thermometer I've been pointing at the casing but obviously that's not telling me what's happening at cell level. Wondering if I need to add a proper temperature sensor setup or whether the integrated BMS handles all that adequately.

Has anyone done any thermal logging on these batteries? I'm half tempted to grab a Victron Battery Sense just to get proper ambient and voltage compensation dialled in, but not sure if that's overkill for a single-battery setup.

Also curious whether anyone's derated their charge current during summer — I'm only pushing maybe 15A max from the panels so it's not like I'm hammering it, but still.

@DefenderLife yeah same deal with mine in the shepherds hut — Drift cells do seem to push mid-30s°C during a heavy bulk on warm days. Doesn't bother me too much tbh, still within LiFePO4 comfort zone.

One thing that helped was dropping my absorption current a touch in the Victron app. Also worth checking your BMS is actually reporting accurate cell temps rather than just ambient — mine was lying to me for weeks 😅

What's your charge current set at relative to capacity? If you're hammering it at 0.5C+ that'll do it.

Hey @DefenderLife — worth checking whether your MPPT charge current is set appropriately for the battery capacity. The general rule of thumb is no more than 0.5C for LiFePO4, so around 100A max for a 200Ah pack, but keeping it closer to 0.2-0.3C tends to be kinder in warmer months. Also, are you running the Victron temperature sensor? Without it the MPPT won't compensate for ambient temperature, which could push cells harder than necessary during summer. Mid-30s as @CrispyWelder mentions is within acceptable range for LiFePO4 (they'll tolerate up to around 45°C charging), but consistently running warm will affect long-term cycle life. What's your actual charge current sitting at?

@DefenderLife worth checking what your charge current is set to relative to the battery's capacity. LiFePO4 cells generally prefer to be charged at 0.5C or below for thermal comfort — so for a 200Ah pack that's ideally no more than 100A, but even pushing 0.2-0.3C can generate noticeable heat in warmer ambient conditions like a garden office in summer.

Also worth logging the actual cell temperatures via the BMS if you have Bluetooth access — mid-30s°C as @CrispyWelder mentions is still within safe operating range, but if you're seeing that consistently I'd look at whether your MPPT is limiting charge current or running flat out. The 100/30 will push the full 30A if your panels allow it, which on a 200Ah pack is 0.15C — should be fine but ambient temperature stacks on top.

Hey @DefenderLife — mid-30s during bulk isn't necessarily cause for alarm with LiFePO4, that's generally within acceptable operating range. What I'd be more interested in is whether the temperature is consistent across the whole pack or if you're seeing hotspots on particular cells. Uneven heating can sometimes indicate cell imbalance developing, especially after eight months of regular cycling. Worth grabbing a cheap IR thermometer and doing a scan across the terminals while it's under load. Also, how's your ventilation around the battery? Even in a garden office setup airflow makes a surprising difference. If you're seeing it creep above 40°C regularly I'd look at throttling your charge current back a touch via the VictronConnect app — easy enough to dial in. What's your rough daily solar input been like lately?

@DefenderLife welcome to the forum — good to see someone asking methodical questions rather than just assuming everything's fine.

One thing I haven't seen mentioned yet: have you actually verified the cell temperature with a separate probe or IR thermometer, rather than relying solely on the BMS reported figure? I've found BMS temperature sensors can sit in awkward spots within the pack, so readings sometimes lag or misrepresent peak cell temps.

Also worth asking — is the warmth consistent across the whole pack, or localised to one end? Uneven heating can flag an imbalance issue that's worth catching early.

I run a Fogstar setup in my shepherd's hut as emergency backup, and I've been curious about long-term thermal behaviour myself. What's your ambient temperature in the garden office? Poor ventilation around the battery can exaggerate things considerably.