Can I mix different battery brands?

Been pondering this for my motorhome setup and thought I'd ask before making a costly mistake.

Currently running a 200Ah LiFePO4 bank made up of four 48V Fogstar batteries wired in parallel. They're about 18 months old and performing well, but I'm looking to expand capacity without replacing the entire lot.

My question is: can I safely add batteries from a different manufacturer — say a Victron or Renogy unit — to the existing Fogstar bank?

I've read conflicting advice online. Some say it's fine as long as voltage and chemistry match (all LiFePO4, all 48V). Others reckon mixing brands causes balancing issues and potential cell damage over time because different manufacturers have slightly different internal resistance and charge profiles.

My system uses a Victron Multiplus-II inverter with integrated BMS, so I'm wondering if that's clever enough to handle mixed brands, or whether it just monitors the total pack voltage without knowing which cells are actually struggling.

Key concerns:

• Will one brand's cells charge/discharge faster than another's?
• Could this create a weak link scenario where the newer battery degrades prematurely?
• Are there any gotchas with warranty claims if something goes wrong?

I'm not looking to save money by buying dodgy batteries — just hoping to expand gradually rather than bin perfectly good kit. Has anyone actually done this successfully, or should I bite the bullet and stick with Fogstar?

Not ideal, mate. I wouldn't recommend mixing different brands in parallel, especially with LiFePO4. Here's why:

Each battery has slightly different internal resistance and voltage characteristics. When you parallel them, the one with lower internal resistance will discharge faster and potentially take on more current than designed. Over time, this causes uneven wear and can damage the weaker unit.

Your Fogstar setup works because they're identical — matched voltage curves and specs. Mixing in say, a Renogy or Battle Born, creates imbalance issues the BMS struggles to manage properly.

If you need more capacity, add the same Fogstar model. If you're already at 200Ah and want expansion, consider series-stacking a second 48V bank instead — much cleaner solution.

What capacity are you actually aiming for? That might open up better options for your motorhome.

Not worth the hassle, honestly. Your Fogstars are solid units with matched BMS specs — mixing in different brands means different cell chemistries, charge profiles, and internal resistance. You'll get voltage drift and one battery doing all the heavy lifting while others sit idle.

Seen it happen on boats loads of times. Parallel needs harmony or you're asking for trouble — faster degradation, potential safety issues, and warranty nightmare if something goes pear-shaped.

If you need more capacity, stick with Fogstar or at least identical models. Swapping the whole bank later is annoying but cheaper than replacing a damaged battery mid-trip.

What size upgrade are you after?

Don't do it. I learned this the hard way with my van conversion — mixed a Renogy with my Fogstars and the BMS systems started arguing with each other. Voltage balancing went to pot, one pack was charging faster than the other.

Parallel configuration means they're all trying to maintain the same voltage simultaneously. Different BMS tuning = different charging curves = potential cell damage over time.

Your Fogstars are matched units, which is exactly what you want. If you need more capacity, stick with the same brand and spec. Easier troubleshooting too when something goes wrong.

If budget's tight, consider waiting and saving for another Fogstar rather than mixing. False economy otherwise — you'll end up replacing cells prematurely.

The real killer is BMS incompatibility — each brand's balancing algorithm works differently, so you'll get voltage drift across your parallel strings and one battery doing all the work while others sulk.

Had this exact scenario with my narrowboat setup years back; mixed a Renogy with my Fogstars and watched the Fogstar's BMS throw a fit every time I charged, causing the whole bank to throttle down to a crawl. Ended up selling the Renogy at a loss.

Your four matched Fogstars are already perfectly happy together — they're spec'd identically so their internal resistance and cell matching actually work properly. Chuck a different brand in there and you're essentially asking two completely different computers to play nicely without a common language.

If you absolutely need more capacity, add identical Fogstar units. Yes, it costs more upfront, but you won't spend months troubleshooting phantom voltage issues or watching your charge controller behave like it's having an existential crisis.

Sticking with your Fogstars is definitely the right call here. The real issue isn't just the BMS disagreeing — it's that you lose any warranty support the moment you mix brands. I learned that the hard way with my shepherd's hut setup.

What people don't always mention is the practical headache: if one battery develops a fault, you can't isolate it without potentially damaging the whole bank. With matched units, you've got consistency in cell chemistry, internal resistance, and thermal behaviour. Mix in a Renogy or similar and you're introducing variables that compound over time.

If you need to expand capacity, honestly just grab another Fogstar 48V to keep everything uniform. The cost difference between that and the risk of BMS conflicts or early cell degradation isn't worth penny-pinching. Your current setup's solid — don't fix what isn't broken.

@OldSailor75 — how much extra capacity are you actually after? Might be worth exploring parallel configuration tweaks before adding different hardware.

Been there with my narrowboat setup. The issue is subtle but serious — while you might get away with it for a bit, the real problem emerges over months of charging cycles.

Each brand's BMS talks to your charger differently. Fogstar uses one algorithm, Renogy another. When you mix them in parallel, they're constantly fighting to maintain their own voltage targets. One battery thinks it's fully charged at 3.65V, another at 3.60V. Result? The weaker one stays perpetually undercharged whilst the stronger one takes all the cycling stress.

@RetiredChef's spot on about voltage drift — you'll watch it creep across your monitoring system if you've got one. The battery that charges slower also discharges slower, creating imbalance that compounds.

For emergency backup, you absolutely need reliability. Stick with your four Fogstars. If you genuinely need more capacity, add another matched Fogstar unit. Yeah, it's pricier upfront, but you won't spend the next two years troubleshooting intermittent issues or replacing a knackered battery at an inopportune moment

The real issue you'll hit isn't immediate—it's creep over time. I'm running three Fogstar 48V units on my narrowboat and they're matched to the amp, which matters when you're living on the boat full-time.

What @RetiredChef and others are saying about BMS is spot on, but there's a practical angle: even if two brands use the same voltage thresholds, they'll charge and discharge at slightly different rates. Over months, one battery ends up carrying more cycles than the other. You end up with one unit degrading faster, and then you're stuck replacing the whole bank piecemeal.

Since you've already got four Fogstars, honestly just stick with them. When you need to expand, grab another Fogstar. They're consistently reliable and you know exactly how they'll behave. The pound you save mixing brands gets swallowed by the grief of managing a Frankenstein setup.

What capacity are you looking to add? Might be worth just doubling down on what works.

You're right to ask before adding to that bank. I've got three Fogstar 48V units in my static caravan setup and learned this the hard way—well, nearly did anyway.

The thing that gets missed in these discussions is cell-level voltage drift. Each battery's BMS will try to balance its own cells, but when you're paralleling different units (even same brand, different batches), they don't agree on what "balanced" means. Over months, you get one unit charging to 3.45V per cell whilst another sits at 3.42V. Sounds trivial, but that's where you get premature degradation and, worse, one unit doing the heavy lifting whilst others coast.

If you're absolutely set on expanding capacity, same batch Fogstars from the same supplier is your safest bet—at least their firmware and cell matching are identical. But honestly? A fifth unit or considering a different chemistry altogether might save you headaches. What's your actual usage pattern? Might be worth exploring whether you need more capacity or better charging strategy.

Been mixing different LiFePO4 brands on my narrowboat for longer than I'd like to admit, and I wouldn't recommend it. The fundamental issue is that each manufacturer calibrates their BMS (battery management system) differently—voltage thresholds, cell balancing algorithms, charge/discharge curves all vary.

What you'll likely experience is one bank charging faster than the other, which means the slower one stays partially discharged while the quicker one cycles harder. Over 12-24 months, that degradation compounds noticeably. The Fogstar units you've got are solid, so I'd strongly suggest just adding more of the same rather than introducing another brand.

If you're wedded to a specific new model, honestly better to retire the existing bank entirely and start fresh. It's not a disaster waiting to happen tomorrow, but it's penny-wise pound-foolish when you're already invested in decent kit.

What capacity are you looking to add? Might be worth exploring whether stacking another Fogstar module actually solves your power requirements or if your charging system is the real bottleneck.

Not trying to repeat what @YorkshireVanLifer and others have said, but wanted to add something I've learned the hard way with my solar setup.

The issue isn't just cell-level creep—it's also that different manufacturers use different internal management strategies. Your Fogstars will have their own BMS logic, and if you introduce a different brand, you're potentially creating a situation where one battery thinks it needs to balance at 55% and another at 48%. Over months this becomes increasingly problematic.

I've got a garden office running mixed Renogy and Victron kit in different subsystems (learned my lesson), and even though they're not directly in parallel, I've noticed the older batteries charge slower because their BMS is more conservative. In a direct parallel setup like yours, that mismatch would accelerate degradation.

If you're genuinely looking to expand your 200Ah bank, I'd bite the bullet and match the Fogstars exactly. It's annoying cost-wise, but you're protecting an already solid investment. Have you considered just adding another pair of those Fogstar units instead?

The real issue you'll hit isn't just the cells themselves—it's the BMS. Each manufacturer's management system has different cell balancing algorithms, voltage thresholds, and response curves. Mixing Fogstar with, say, Renogy or Battle Born means you've got two competing systems trying to manage the same pack.

I learned this the hard way on my narrowboat. Added a different brand 48V unit to my existing bank and within six months the older batteries were sitting at lower state of charge whilst the new ones cycled harder. The BMS units were literally fighting each other over what constituted "full" and "empty."

If you've got space, your best bet is running separate battery banks with their own chargers and Victron MultiPlus managing them independently. It's more wiring, but you get reliability and you can replace failed units without the domino effect.

Stick with matching Fogstar units if you can. They're not the cheapest, but that consistency actually saves money long-term by avoiding premature cell degradation.

Mixing brands is asking for trouble with LiFePO4—your Fogstars have their own BMS tuning, and chucking in different ones creates voltage balancing nightmares. Stick with your existing setup, or upgrade the entire bank together. Your wallet'll thank you later.

Had this exact dilemma with my caravan setup. The balancing issue @ExSquaddie49 mentioned is real—I've seen Fogstar and Renogy packs fight over charge rates even when paralleled properly. Stick with your Fogstars if you need more capacity. Going the same brand route just saved me weeks of troubleshooting.