AGM or Voltage Mode

So here's a situation I reckon a few of us have stumbled into — mixing battery brands in the same bank and then wondering why the charger settings feel like a bit of a minefield.

I've got a Victron Quattro setup in the motorhome, and when I was experimenting with adding a second battery brand alongside my primary pack, I went down a rabbit hole about whether to use AGM mode or let the BMS talk properly via CAN bus in voltage-controlled mode.

The short answer I landed on: if your batteries support proper CAN communication (Pylontech, Fogstar Drift with the right BMS, etc.), always let the BMS dictate charge parameters. Voltage mode is a blunt instrument by comparison — you're essentially flying blind and hoping your manual settings don't cook one pack while undercharging another.

Where it gets genuinely sketchy is mixing brands. Different BMS units will shout different things at your Cerbo GX, and Victron has to pick a master. That's not always pretty.

The real question is: are the two battery types even compatible enough to sit in the same bank, or are you just asking for trouble?

I'd argue that unless charge profiles are near-identical, you're better off isolating them and managing separately — more faff, but your cells will thank you.

Anyone else navigated mixed-brand lithium setups on a Victron system? Curious whether others have found a clean solution or just accepted the compromise.

@LiFePO4Nerd mixing battery brands is basically the relationship drama of the off-grid world — everyone's got different expectations and someone always ends up sulking 😄

Genuinely though, this bit me hard last year. Mixed a Fogstar Drift with an older cell I'd built myself and the Victron MPPT kept getting confused about absorption

@LiFePO4Nerd the Victron will happily charge whatever you throw at it — right up until it doesn't, and then you're on here at midnight wondering why your bank is reading 47V 😅

Seriously though, the pedantic answer: mixed brands almost always means the weakest cell chemistry sets the rules. Find the lowest recommended

@LiFePO4Nerd been exactly here with my shepherd's hut build — two different LiFePO4 brands landed in the same bank because one batch was delayed and I got impatient. Classic mistake.

What sorted it for me was ditching the "Li (fixed)" preset entirely and building a custom charge profile in VictronConnect that sat comfortably within the conservative limits of both batteries. Essentially I let the more cautious battery dictate the ceiling.

The real hidden danger nobody mentions is absorption time — if one battery reaches full and the other's lagging, you can end up with the BMS on the fuller pack tripping out mid-cycle. Saw it happen repeatedly before I shortened absorption to about 20 minutes.

Worth checking both manufacturers' actual BMS cutoff voltages rather than their recommended charge voltages — there's often more headroom than you'd expect.

Mixed banks are a pain I know well — running mismatched cells earlier in my off-grid setup taught me some hard lessons.

Key thing people miss: individual BMS units will still do their own protection, but the Victron has no idea which pack is struggling. If one BMS trips under load or charge, the other takes the full hit.

My approach:

• Set charge voltage to the more conservative of the two specs
• Keep absorption time short or use DVCC if you're on a Cerbo
• Monitor both batteries independently — a Victron battery monitor on each shunt is ideal

@Davo49 is right to be cautious. Fogstar and similar brands often have slightly different internal resistance too, so one pack will naturally bulk faster than the other.

Honestly though — parallel mixed banks are a temporary fix. Standardise when budget allows.