SmartLithium 330Ah deep-discharge recovery: is 0.5C essential

Had a similar nightmare on the narrowboat last winter — bilge pump controller failed silently overnight and I came back to find my 200Ah Fogstar Drift cells sitting at 2.1V per cell. Not pretty.

The question I kept hitting was whether throwing a gentle recovery charge at them (something like 0.1C or even lower) was actually safer than the often-cited 0.5C recommendation, or whether getting them back above the protection threshold quickly was the priority to avoid further degradation.

What I eventually did:

• Used a Victron IP22 on its lowest setting with a custom absorption voltage
• Monitored cell deviation closely via the SmartShunt
• Took about 3 hours before the BMS would even "wake up" properly

The batteries did recover, but I've always wondered whether I stumbled through it rather than actually doing it right.

For a 330Ah SmartLithium specifically, 0.5C would be 165A — that feels aggressive for cells that have been sitting badly discharged. Victron's own docs are a bit vague on this for the recovery scenario rather than normal cycling.

Has anyone here done a proper recovery on the SmartLithium 330Ah bank? Curious whether:

1. You stuck to the 0.5C recommendation or went lower
2. Whether the BMS gave you any grief during the process
3. If capacity ever fully returned afterwards

I'm also wondering if this is different for boat installations versus static setups — the temperature variation in a bilge might complicate things further.

Would be good to get some real-world accounts rather than just datasheet theory.

@PeteJames that 2.1V/cell figure is genuinely alarming — you're well into copper dissolution territory at that depth.

One thing worth adding to the recovery conversation: recovery charge rate matters less than your initial absorption voltage ceiling. I recovered a 280Ah Fogstar pack from ~2.4V/cell last year using a Victron SmartSolar in absorption-limited mode, starting at around 0.05C and only stepping up once cells balanced within 20mV of each other via the BMS telemetry.

The 0.5C recommendation exists primarily to generate enough heat internally to drive electrochemical recovery — but in a cold narrowboat bilge, you're fighting that anyway. I'd argue 0.1–0.2C with careful voltage monitoring is more pragmatic and puts less stress on already-compromised cells.

Did your Fogstar BMS log the low-voltage event duration? That's the real indicator of whether the cells are worth pursuing or binning.

@PeteJames been there with my narrowboat setup — very similar story, pump controller fault dragged my Fogstar cells down to around 2.3V before I caught it.

What saved mine was recovering at an absolute crawl — I started at roughly 0.05C rather than the 0.5C figure you often see quoted. The Victron SmartSolar let me set a custom absorption voltage and I held it there for a good few hours before stepping up.

Key thing I'd add: check internal resistance before declaring the pack recovered. I used a basic YR1035+ meter across each cell. Two of my eight cells showed noticeably elevated IR even after voltage recovered — those needed watching closely for the next few months.

@EcoFlow_Queen is right about copper dissolution being the real concern at 2.1V — worth doing a capacity test at low rate once you think it's stable.

@PeteJames did your Fogstar cells actually recover properly after that? I'm curious what recovery procedure you used — did you do a slow trickle charge first or go straight to a normal charge rate?

Asking because I've got a motorhome setup and I'm always worried about a similar scenario if something drains the bank overnight whilst I'm parked up remote. My Victron BMV-712 has a low voltage alarm set but if the BMS cuts out before the alarm triggers I'm not sure how much protection that actually gives me in practice.

Is the 0.5C recovery rate genuinely necessary or would something lower like 0.1C be safer for badly depleted cells? Wondering if the Victron MPPT has a recovery mode that would be suitable or whether you'd need a dedicated recovery charger.

@PeteJames the 0.5C recovery current debate is genuinely nuanced. At 2.1V/cell you're in a bad spot, but I've successfully recovered cells from similar depths using a staged approach rather than strict 0.5C throughout.

My procedure on a comparable Fogstar incident:

1. Trickle at 0.05C until cells reach ~2.8V — this is the critical phase where you're checking for internal shorts developing
2. Step to 0.1C up to 3.0V, monitoring cell temperature obsessively
3. Normal charge only once you're confident voltage is rising linearly

The 0.5C figure gets quoted as a maximum for recovery, not a target. Slower is genuinely safer here — copper dissolution risk increases dramatically if you push current through a potentially compromised cell.

Capacity loss is almost inevitable after 2.1V, but @Squib the cells can absolutely be usable — I retained about 87% on mine after three conditioning cycles.

@PeteJames this is relevant to me — fitting out a van conversion and genuinely worried about over-discharge scenarios when I'm parked up for weeks unattended.

Quick question: does the Victron SmartLithium BMS give you any useful telemetry after a deep discharge event, or does it basically just lock you out until recovery? Wondering whether I'd even know the exact per-cell voltage I'd bottomed out at, or whether that data is lost once the BMS cuts off.

Also curious whether anyone's found a meaningful difference between recovering at 0.1C versus 0.5C in terms of capacity retention long-term — not just whether the cells work afterwards, but whether you actually lose measurable Ah from the pack permanently.