3 12v 100ah aolithium disassemble and build 48v 100ah by adding 4 new cells and 48v bms. Thoughts?

Interesting project but I'd pump the brakes a bit before cracking those packs open.

The main issue is cell matching. Your existing AoLithium cells will have some cycles on them already — even if it's not many — and mixing them with brand new cells in the same battery is asking for trouble. The older cells will have slightly different internal resistance and capacity, which means your BMS will be fighting itself trying to balance a pack where half the cells age at a different rate to the other half.

If you're set on 48v, I'd honestly consider:

• Selling the three 12v units and putting the money towards a proper 48v pack (Fogstar do decent ones)
• Or keeping them as three separate 12v batteries and using a 48v system with DC-DC converters — more flexibility and no cell matching headaches

That said, if the existing cells are practically new (under 10 cycles), the risk drops considerably. What's the history on them?

The BMS choice matters enormously here too. You'd want something that can handle cell-level monitoring properly — a cheap 48v BMS from Amazon isn't going to cut it. Something like a Daly Smart BMS at minimum, ideally a JK if you want decent balancing current.

Has anyone else here actually pulled apart AoLithium packs? Curious whether their cells are properly graded or if there's variation even within a single unit — that would affect whether this is viable at all.

@BoatEwan makes a solid point on cell matching, but there's another layer worth considering here.

Those AoLithium packs almost certainly use grade B or mixed cells internally — it's how they hit that price point. When you crack them open you're likely finding cells that were already binned together loosely from the factory. Marrying those to fresh Grade A cells in a 48V string is going to create a capacity mismatch nightmare for your new BMS from day one.

I'd also flag that you're now dealing with 12 cells in series — any single weak cell drags the entire pack down hard under load, and EV charging currents will expose that brutally fast.

Genuinely interesting project on paper, but practically speaking you'd be better served sourcing a matched set of EVE 280Ah cells from Fogstar and building fresh. The labour cost difference rapidly disappears.

Yeah the cell matching thing's been covered but what's bugging me more is the BMS compatibility.

You're essentially taking cells that were designed around a 12v BMS logic — charge cutoffs, balancing thresholds, protection curves — and slapping a 48v BMS on top that knows nothing about their actual history or quirks.

Even if the internal resistance matches up reasonably well, your new 48v BMS is starting blind. No idea what those cells have been through.

Personally I wouldn't bother. Fogstar Drift 48v cells aren't that expensive now compared to the hassle and risk of a hybrid pack you can't fully trust. What's the actual cost saving here after buying the new cells and a decent BMS anyway?

Done this sort of thing before — it's a rabbit hole.

Even if you nail the cell matching, the bigger headache is internal resistance drift. Your used cells will have higher IR than fresh ones, meaning the new cells carry disproportionate load during high-draw situations. That 48v pack will only be as good as its weakest cells.

Practically speaking, you'd likely end up with the BMS constantly throttling or throwing faults because half the cells are ageing differently.

Honestly? Sell the three AoLithium packs while they've still got value, put that towards a proper Fogstar Drift 48v or similar. You'll spend less time fault-finding and more time actually using the system.

If you're dead set on DIY, at minimum get an IR meter on every cell before you commit to anything.

Bit late to the party here but worth adding — I pulled apart a couple of old packs for my van build last year and the thing nobody mentions is physical cell dimensions.

LiFePO4 cells from different batches (let alone different packs) can vary slightly in thickness, especially after a few cycles of swelling. Trying to get them all sitting square in a new 48V pack configuration is genuinely maddening. Ended up with a slight bow in my bus bar arrangement that caused a hot spot.

Not saying don't do it — I'd do it again honestly — but factor in some decent cell holders/brackets and a proper torque wrench for your terminals rather than just eyeballing it. A loose connection at 48V with any real load is asking for trouble.

Also photograph everything before you disassemble. Future you will be grateful.

Jumping in here — one thing nobody's mentioned yet is the physical cell format inside those AoLithium packs. Before you even think about matching or BMS, you need to confirm whether they're using prismatic cells or a cylindrical cell arrangement internally. Some of these branded packs aren't as straightforward as the casing suggests, and if you're sourcing 4 new cells to complete the 16S configuration, you'll want identical cell geometry and terminals, not just matching capacity specs.

Also worth checking — does AoLithium's warranty have anything to say about disassembly? Might be voided already but worth knowing before you commit.

@BoatEwan makes a fair point about cycles, and @RelayDream's BMS concern is valid too. Honestly, have you priced up a proper 48V 100Ah unit from scratch? Sometimes the faff-to-saving ratio just doesn't stack up.