How can the battery be woken up and charged by the SmartSolar MPPT？

Had this exact headache with my shepherd's hut setup last winter. Battery got down to nothing after a few cloudy weeks and the Victron SmartSolar just sat there doing nowt — couldn't push any charge into a pack that had essentially gone into protection mode.

Few things that worked (or didn't) for me:

• Manual wake-up first — some BMS units have a physical button or need a small external charge source to "wake" them before the MPPT can see the battery properly. I used a basic bench charger briefly just to nudge the voltage up enough for the SmartSolar to recognise it
• MPPT rebulk settings — worth checking your rebulk voltage threshold isn't set too high. If the battery voltage is below that threshold the controller won't even attempt to charge
• VE.Direct / Cerbo comms — with everything networked through the Cerbo you'd think it'd be smarter about this, but in my experience the MPPT still needs to "see" a minimum voltage on the battery terminals regardless of what the GX is telling it

Anyone running a Fogstar or similar lithium pack — does your BMS have a dedicated wake-up input? That seems to be the cleanest solution rather than faff.

Also curious whether anyone's used the Street Light or Load output on the SmartSolar to trickle a tiny bit back through as a workaround — seen it mentioned elsewhere but never tried it myself.

What's everyone else's go-to method for this? Feels like it should be more straightforward given the kit costs what it does.

@StormyViking classic "the patient is too dead to accept medicine" problem — Victron calls it the low voltage wake-up issue, and the fix on most SmartSolar units is to enable the MPPT's battery wake-up / force charge feature in VictronConnect, which pulses a small current to nudge a deeply discharged lithium back above its BMS reconnect threshold.

Worth noting: if it's a Fogstar or similar LiFePO4 with a BMS that's fully tripped, you might need to manually wake the BMS first with a 12V bench supply or even a small lead-acid briefly paralleled — completely normal procedure, not a bodge.

Also double-check your absorption/float voltages match your battery spec; a misconfigured Victron profile is surprisingly often the real culprit hiding in plain sight.

Been there with my motorhome — the trick is Victron's "battery voltage too low" recovery mode: in VictronConnect, enable the "allow to charge lower battery voltage" option, or manually feed it a small boost from a leisure battery via jump leads just long enough to nudge it above the MPPT's wake-up threshold (usually ~10.5V for a 12V system).

Alternatively, a cheap bench power supply or even a basic Halfords smart charger on its recovery/recondition mode will coax it back to life, then hand it over to the SmartSolar.

Worth checking your battery isn't actually dead-dead first — a deeply sulphated AGM might accept surface voltage but hold nothing. If it's a Fogstar Drift LiFePO4, the BMS may have tripped entirely and needs a dedicated lithium wake-up procedure.

@MarineGeoff is on the right track but worth clarifying the mechanism — the SmartSolar sends periodic "wake-up pulses" to check if the battery can accept charge before committing to full operation.

If that's still not recovering it, what's worked for me on my van build is using a bench power supply or even a car battery to float the dead pack up to around 12.0–12.4V first. Even 20–30 minutes at low current is enough to convince the MPPT the battery is "alive."

Fogstar and similar LiFePO4 packs also have internal BMS low-voltage cutoffs that the MPPT can't override — if that's tripped, no amount of solar trickery helps until you address the BMS directly, sometimes via a dedicated balancer/activator or manufacturer reset procedure.

What battery chemistry are you running? Makes a significant difference to the recovery approach.

@ExBrickie31 has covered the pulse mechanism well. Worth adding that the threshold voltage where the SmartSolar gives up entirely is around 2V per cell (so ~12V nominal = roughly 10.5V cutoff) — below that you'll need to manually pre-charge the battery with a bench supply or a dedicated charger like the Victron IP65 set to its recondition mode before the MPPT will take over.

Also check your VictronConnect app → SmartSolar settings → "Battery voltage" dropdown — if it's set to auto-detect and the battery is truly flat, it sometimes misidentifies the bank entirely and refuses to charge. Manually forcing it to 12V (or 24V if that's your system) sorts this immediately.

Fogstar and BMS-equipped lithiums add another layer — the BMS itself may need waking separately before any charger sees the pack.

Good shout from @GoldenTrekker on the threshold point. One thing nobody's mentioned yet — if the pulses genuinely aren't working and you're in a hurry, a small donor battery temporarily paralleled to the flat pack gives the MPPT just enough voltage to "see" it and begin proper charge. I've done this twice on the boat when lithiums have sulked over winter.

Also worth checking in VictronConnect that your battery minimum voltage setting isn't set too conservatively — I've seen installs where someone's cranked it up for "protection" and accidentally put it above the recovery pulse threshold, which means the controller just keeps refusing indefinitely.

If it's a Fogstar or similar smart lithium with a BMS, the BMS itself may need a manual reset button press before any external charging will take.