Cells arriving tomorrow — do I need to top balance before first use?

Yes, absolutely top balance first — don't skip it, you'll regret it.

When I got my first batch of Fogstar cells I was impatient and just chucked them straight in. BMS was tripping constantly for the first week because the cells were all over the place. Wasted days of good sun basically doing nothing.

Top balancing gets everything sitting at the same voltage before you start cycling them. Your BMS can then do its job properly rather than fighting against wildly uneven cells from day one.

The process is pretty straightforward:

• Charge each cell individually to 3.65V (for LFP)
• Let them sit until the current drops right off
• Then connect them all up and let them settle overnight

Takes a bit of patience but honestly worth every hour. My Victron Lynx setup has been rock solid ever since I started doing it properly with new cells.

Only exception I'd say is if you're buying pre-matched/pre-balanced cells from a reputable supplier — even then I'd still check voltages on arrival and at least parallel them up overnight before building the pack.

What cells are you getting? Grade A or the cheaper B-grade stuff? Makes a difference to how much variance you might be starting with. Some batches I've seen arrive surprisingly close, others are a right mess.

Anyone else had good or bad experiences skipping the top balance stage? Curious whether it's just my luck or a common issue.

@PanelMatt I'll add the why to your very correct "just do it" advice.

Cells from the factory typically arrive at different state of charge — sometimes wildly so. Your BMS sets protection thresholds per cell, not per pack. So if one cell wanders 200mV above its neighbours, the BMS sees an overvoltage event and trips, even though the pack as a whole looks perfectly reasonable.

Top balancing brings every cell to the same ceiling simultaneously. After that, your passive balancer (assuming you've got one built into the BMS — most decent units like the Daly or JK have it) keeps them tracking together during normal cycling.

I did mine on a bench power supply set to 3.65V per cell, limited to about 5A. Took an afternoon. Boring, but considerably less boring than debugging a mystery-tripping BMS at midnight in a shepherd's hut. Ask me how I know.

Great points from @PanelMatt and @CopperWelder already covering the what and why.

One practical thing worth adding: the process takes longer than most people expect. My first top balance on 280Ah EVE cells took nearly 48 hours at low current (around 5A into a parallel lash-up) before voltages truly converged and held stable at 3.65V.

A few tips from my static caravan build:

• Use a bench power supply in CV mode rather than a charger — far more control
• Monitor individual cell voltages throughout, not just the group terminal
• Don't rush it by pushing higher current; slow and steady gets genuine convergence
• Once done, check resting voltages after an hour — if any cell drifts noticeably, investigate before building your pack

The Fogstar cells I used were actually pretty well-matched out of the box, but top balancing still made a meaningful difference to BMS behaviour afterwards.

Good advice from everyone so far, but I'd add one pedantic but important clarification: top balancing and storage voltage are two different things.

Cells are often shipped at ~50% SoC for safety reasons, so they won't arrive balanced or at full charge. You need to bring all cells to 3.65V individually (not just charge the pack as a whole) before parallel-linking them for the balance soak.

I use a bench power supply set to exactly 3.65V per cell — my Victron setup can't do this stage properly on its own. Takes patience but you only do it once.

@VanGill makes a fair point on the practical side — I'd just emphasise that rushing the balance soak (less than a few hours at absorption) defeats the purpose entirely.

How long does top balancing actually take in practice? I've got 280Ah EVE cells arriving for the narrowboat and I'm trying to work out if I need to do this over a weekend or if it's a days-long job.

Also — what do people actually use to do it? I've just got a basic bench power supply. Is that sufficient or do I need something more specific? Seen some mention of using a Victron charger in absorption mode but that seems overkill for a one-off job.

@NaeClue13 good point on the storage voltage distinction, that's caught me out before on smaller lithium packs.