Victron smallBMS NG: Compact BMS for Lithium NG

The Victron smallBMS NG is the simplest battery management system for Victron Lithium NG batteries. NG batteries have no built-in BMS, so they need one of Victron’s NG BMS units to switch chargers and loads off when a cell goes out of range. The smallBMS NG does that with signal outputs instead of carrying the battery current itself. Here’s what Victron’s datasheet says.

Victron smallBMS NG: Specs


Operating voltage	8–70V DC
Load disconnect output	Vbat – 0.1V, 1A max (not short-circuit protected)
Charge disconnect output	Vbat – 0.1V, 500mA max (not short-circuit protected)
Pre-alarm output	500mA max
Consumption	3mA on; 1.2mA at low cell voltage or remote off
Operating temperature	-20 to +50°C
Protection	IP20
Size / weight	106 × 42 × 23mm, 0.1kg

Source: Victron smallBMS NG datasheet. The power supply cable and fuse (0.3–2.5A) are not supplied.

How It Works

The smallBMS NG reads cell data from the daisy-chained NG battery cables. Then it switches two outputs:

Load disconnect goes to the remote on/off of a Smart BatteryProtect, an inverter, a DC-DC converter or other loads. At 1A it can even drive a high-current relay or contactor.
Charge disconnect goes to chargers such as the Smart IP43, a Cyrix-Li-Charge or a BatteryProtect. Victron warns it can’t power an inductive load like a relay coil.

The pre-alarm fires at least 30 seconds before the load output shuts off, to drive a buzzer, LED or relay.

Other Features

Bluetooth setup, monitoring and firmware updates in VictronConnect, with Instant Readout of SoC and temperature.
Configurable discharge floor: set a minimum SoC. A low-SoC alarm then disconnects the loads.
Remote on/off terminal for a main system switch.

The MultiPlus Caveat

Victron says the smallBMS NG “lacks a VE.Bus interface and is therefore not suitable for use with VE.Bus MultiPlus and Quattro inverter/chargers.” For those, use the VE.Bus BMS NG or the Lynx Smart BMS NG.

smallBMS NG vs the Original smallBMS

The original smallBMS is for Victron’s Lithium Smart batteries. The NG version is only for Lithium NG batteries, and Victron’s datasheet warns not to confuse the two ranges.

Who It’s For

Vans and small boats with NG batteries, DC loads, an MPPT and a DC-DC charger, but no MultiPlus.
Systems where every charger and load has a remote on/off input.

Good to Know Before You Buy

No VE.Bus.
Outputs aren’t short-circuit protected.
It doesn’t carry battery current, so you need BatteryProtects, relays or remote-controlled devices.

Want the source figures? The smallBMS NG page on Victron’s site has the datasheet.

Worked Example: A Van With a smallBMS NG

A camper van with two 12.8V 200Ah Lithium NG batteries, a SmartSolar MPPT 100/30, an Orion XS DC-DC charger, a 12V fridge and a small Phoenix inverter:

The two batteries’ BMS cables daisy-chain together and run to the smallBMS NG.
The charge disconnect output goes to the remote on/off terminals of the SmartSolar MPPT and the Orion XS, so both stop charging if a cell goes high or the battery gets too cold to charge.
The load disconnect output goes to a Smart BatteryProtect feeding the fridge and DC loads, and to the Phoenix inverter’s remote on/off.
The pre-alarm drives a small buzzer on the dashboard, giving at least 30 seconds’ warning before the loads switch off.
The smallBMS NG’s own draw of 3mA works out to about 0.07Ah a day, a tiny fraction of the 400Ah bank (estimate).

Worked Example: Setting a Discharge Floor

Setting the discharge floor to 20% on that 400Ah bank keeps about 80Ah, or roughly 1kWh, in reserve (estimate). When state of charge drops to the floor, the low-SoC alarm disconnects the loads, leaving enough energy to restart charging from solar or the alternator the next day.

Wiring Checklist

Daisy-chain the NG batteries’ BMS cables and connect the last one to the smallBMS NG.
Power the smallBMS NG from the battery with an inline fuse between 0.3A and 2.5A, as the datasheet specifies. The cable and fuse are not supplied.
Wire the load disconnect to each load device’s remote on/off, or to a Smart BatteryProtect.
Wire the charge disconnect to each charger’s remote on/off. Use a non-inverting remote cable where the manual calls for one.
Connect the remote on/off terminal to a main system switch if you want one.
Open VictronConnect, pair over Bluetooth and update the firmware.

Devices That Pair Well

Chargers: SmartSolar MPPTs, Orion XS and Orion-Tr Smart DC-DC chargers, the Smart IP43 charger, and Cyrix-Li-Charge relays.
Loads: Smart BatteryProtect, Phoenix inverters and Orion DC-DC converters with remote on/off.
Monitoring: a SmartShunt for precise current readings, or a GX device for VRM.

Choosing an NG BMS

System	Good fit
—	—
DC loads, MPPT and DC-DC charger, no VE.Bus	smallBMS NG
MultiPlus or Quattro on VE.Bus	VE.Bus BMS NG
Larger system wanting a built-in contactor and GX integration	Lynx Smart BMS NG

Installation Notes

Mount it in a dry location, since it’s IP20.
At 106 × 42 × 23mm and 0.1kg, it fits beside a fuse box or busbar.
Keep the operating range of -20 to +50°C in mind for unheated spaces.
Label each signal wire so later changes are easy.

Why NG Batteries Need an External BMS

Lithium NG batteries balance their own cells and report cell data, but they don’t have a switch inside to cut off chargers or loads. The external BMS reads that data and tells the rest of the system when to stop. With the smallBMS NG, that control is done through low-current signal wires, which keeps the unit small and lets each charger and load switch itself off.

Checking the System in VictronConnect

After setup, Instant Readout shows state of charge and battery temperature on the VictronConnect device list without opening the device. Check that the charge and load outputs change state when you switch the remote on/off off, so you know every device responds before relying on it.

FAQ

Can I use the Victron smallBMS NG with a MultiPlus-II?

No. Victron says to use a BMS with VE.Bus instead.

Does it work with Lithium Smart batteries?

No, it’s for Lithium NG batteries only.

Does the smallBMS NG measure battery current?

No. It reads cell data from the NG batteries. Add a SmartShunt for accurate current and state-of-charge readings across the whole system.

Can the charge disconnect switch a relay?

No. Victron says it can’t drive an inductive load like a relay coil. Use the load disconnect output, which handles up to 1A, for that.

How many NG batteries can it manage?

Several NG batteries can be daisy-chained to one smallBMS NG. Check the Lithium NG datasheet for the limit for your battery voltage.

Sources: Victron smallBMS NG datasheet; Lithium NG batteries datasheet; product pages, victronenergy.com, accessed Oct 2026.