Thermo Technica WG-BC900M Smart DC-DC Charger for Modern Off-Grid Builds

The Thermo Technica WG-BC900M smart DC-DC charger is a fully programmable 900W battery-to-battery charger built for owners who need real control over how their leisure battery is fed on the move.

Unlike fixed-profile chargers, this unit talks to your laptop over RS485 Modbus RTU, so you can fine-tune voltages, currents, alarms and timing to match exactly the battery in your vehicle.

So whether you run a single LiFePO4 leisure battery or a 48V touring setup, the WG-BC900M adapts to it.

Designed for motorhomes, caravans, campervans, narrowboats and marine applications, this charger pairs serious hardware with a brushed aluminium finned heatsink and screw-terminal connections with a software-driven brain. As a result, you get the protection of an industrial-grade unit and the flexibility of a hobbyist setup in one box.

Why Choose a Smart DC-DC Charger Over a Standard One?

Modern vehicles use Euro 6 smart alternators that drop voltage to save fuel. Consequently, a basic split-charge relay or older battery isolator cannot keep your leisure battery topped up properly. A smart DC-DC charger like the WG-BC900M actively boosts and regulates voltage from the starter battery, which protects your alternator and pushes a full, fast charge into your auxiliary bank even on short drives.

Moreover, because lithium batteries demand precise charge profiles, fitting a programmable charger is the safest way to get the full cycle life out of your LiFePO4 or Li-NCM pack. The WG-BC900M lets you set under-voltage cut-off, over-voltage protection, recovery thresholds and float voltages independently for both input and output terminals.

Built for Lithium Leisure Battery Systems

The WG-BC900M is at home with the latest lithium leisure batteries. Select from five battery chemistries in the Windows software:

Li-NCM — Lithium Nickel Cobalt Manganese
Li-LFP (LiFePO4) — Lithium Iron Phosphate, the leisure battery standard
La-GEL — Sealed Gel lead-acid
La-AGM — Absorbed Glass Mat lead-acid
DC mode — Generic DC power supply mode

Each profile loads a tailored charging curve, so you simply pick your battery type and let the charger do the rest.

RS485 Modbus RTU Communication and Windows Software

Every WG-BC900M ships with full Modbus RTU support over an RS485 interface (9600bps, 8-N-1). Connect a USB-to-RS485 adapter to any Windows PC, run the included WG-BC900M-Window utility, and you can monitor live voltages, currents, temperatures and fault states in real time. In addition, you can set:

Forward and reverse output start-up delays
Soft-start current ramp times
Auto-switch turn-on and turn-off voltages
Charging and full-charge LED indicator thresholds
T1, T2 and Ta over-temperature protection trip points

OTA firmware upgrade is also supported, so the unit stays current as new battery profiles roll out.

Download WG-BC900M Windows Software V1.02

Click to Download the File

Bi-Directional Operation for Dual-Bank Setups

One of the standout features of this smart DC-DC charger is its true bi-directional mode. Terminal A and Terminal B can both act as input or output, with the unit automatically switching direction based on configurable voltage thresholds.

Therefore, you can build a setup where the alternator charges your leisure bank while driving, then the leisure bank tops up your starter battery if it ever runs low, all from a single device.

Technical Specifications

Specification	Detail
Model	WG-BC900M
Maximum Power	900W
Supported Voltages	12V / 16V / 24V / 36V / 48V / 60V / 72V / 10–50V
Battery Types	LiFePO4, Li-NCM, GEL, AGM, DC
Charging Stages	Pre-charge → CC → CV → Float → Complete
Charging Modes	Forward, Reverse, Automatic, Manual, Peripheral
Communication	RS485 Modbus RTU, 9600bps, 8-N-1
Configuration	Windows software (WG-BC900M-Window V1.02)
Firmware Update	OTA via RS485
Protections	Over/under-voltage, short-circuit, over-temperature, and derating
Temperature Sensors	T1, T2, Ta with programmable trip points
Indicator	Tri-colour LED (charging / full / fault)
Housing	Finned aluminium heatsink, screw terminals
Connector	6-pin signal cable (RS485+, RMT, PG, ACC, RS485-, BAT-)

What’s in the Box

1 × Thermo Technica WG-BC900M smart DC-DC charger
1 × 6-pin signal cable (RS485, RMT, PG, ACC, BAT-)
1 × Quick-start guide
Digital download: Windows configuration software + full Modbus protocol

Frequently Asked Questions

Is the WG-BC900M suitable for smart alternator vehicles?

Yes. The unit actively boosts and regulates voltage from a Euro 6 smart alternator, delivering a stable, fast charge to your leisure battery regardless of how the engine management trims the alternator output.

Can I use this DC-DC charger without a computer?

Absolutely. The factory defaults cover the most common 12V LiFePO4 leisure battery setups. However, plugging in via RS485 unlocks full customisation, live monitoring and OTA updates.

Does it work with solar?

The WG-BC900M is a dedicated battery-to-battery charger, not an MPPT controller. For solar, pair it with a separate MPPT solar charge controller. Both can charge the same leisure battery side by side.

What size cable should I use?

For a 900W unit running near full output on a 12V system, use a minimum of 25 mm² (3 B&S) battery cable, with appropriately rated fuses at both terminals. Refer to our battery cables and lugs for compatible options.

Is there a warranty?

Yes. The Thermo Technica WG-BC900M is covered by our standard UK warranty. Register your product on our warranty page after purchase.

Ready to Upgrade Your Off-Grid Power?

Whether you are converting a van, refitting a motorhome or building out a narrowboat, the Thermo Technica smart DC-DC charger gives you industrial-grade control at a fair price. Pair it with a quality lithium leisure battery and an inverter from our DC-DC battery chargers range to complete the build.

“New to DC-DC charging? Read our 2026 buyer’s guide first.”

Thermo Technica WG-BC900M 900W Smart DC-DC Charger