Auto-Trail • Expedition • 2026

First, an alert appears on the control panel's screen, warning that the battery needs recharging.

The system alerts again, then switches off every circuit it controls to stop further discharge - though anything wired directly to the battery, bypassing the control system, will keep drawing current regardless.

Steer clear of frequent deep discharges, and try to keep it sitting at a partial charge - ideally somewhere between 40% and 80% - rather than running it right down. Don't treat Under Voltage Protection (UVP) kicking in as your cue to recharge; by then it's already past where you want to be.

Most Sargent systems use a PX300 or PF200 battery charger. If yours has a different charger fitted, check with that charger's own manufacturer for Lithium compatibility. The PX300's charging profile suits many leisure-industry Lithium batteries that have their own internal Battery Management System (BMS) - its charging profile and voltages are available as a downloadable attachment on the PX300's own product page, though you'll still need to confirm suitability directly with your chosen battery's manufacturer.

Systems that use a PX300 include the EC800, EC700, EC600, EC500, EC400 series, EC400+ and EC328. If your system doesn't have a PX300, its charger will run a fixed 13.8V, which generally isn't suitable for fully charging a Lithium battery - and switching to Lithium may also mean you need a DC-DC charger to keep the charging current within limits.

We don't endorse any particular make or model, but the PX300 charger (fitted across the EC400/EC400+, EC500, EC600, EC700, EC800 and EC328 systems) suits the great majority of good-quality AGM batteries sold in the UK. Its charge profile is included in the instruction manual attached to its product page - if you're at all unsure whether a battery is compatible, check with that battery's own distributor or manufacturer first.

Installation and wiring: wire the extra LB series battery into the vehicle's 12V system first, and connect its magnetic communication cable to the Sargent Control System's CAN bus. Before paralleling two batteries, make sure both are fully charged to the same voltage, to avoid a big rush of current between them the moment they're connected.

Changing the battery address: adding a second battery in parallel means changing its communication address from the default '1' to '2', so both can talk to the system at once - only have the battery you're changing connected via its comms cable while you do this (the steps are the same on the 4" EC940 and 7" EC970 screens).

Configuring single or dual batteries: the display needs the Sargent Lithium+ battery switched on in the ADVANCED SETUP menu first, or it won't communicate with it - choose Lithium+ for a single battery, or Lithium+ x2 for a dual setup.

Information displays: once configured, extra screens appear in the Control Panel's POWER menu. On the EC940's 4" display, a dual setup's two batteries are combined into one figure (two 70Ah batteries show as 140Ah total); on the EC970's 7" display, tapping the battery symbol switches between Battery 1 and Battery 2's individual readings.

Installation and wiring: mount each sensor on the tank's top surface, close to the middle, to avoid reflections off the tank wall and reduce variation when parked on a slope. Fit a side-mounted overflow too, so a sensor doesn't end up sitting underwater after filling and skewing its readings - and note the sensor isn't suitable for tanks with a sloped or irregular base, which will also throw off readings.

Configuring the sensors: enable the Sargent Ultrasonic Water Sensors in the ADVANCED SETUP menu first so the display can communicate with them, and enable the relevant tank too for its level to actually show - any tank not configured for ultrasonic sensing is assumed to have a traditional rod/stud sensor instead.

First-time calibration: the sensor automatically starts calibrating its tank depth the first time it gets 12V power, so make sure it's fitted and the tank is empty beforehand for an accurate result. Once calibrated, it sends regular readings (roughly every 5 seconds for fresh tanks, 10 for waste) - and since it can't read fluid closer than 30mm to its own face, the 100% level gets set 30mm below the measured tank depth. Re-calibration can be triggered any time from the Advanced Setup menu, either automatically (again, with the tank empty first) or manually if you'd rather enter the tank depth yourself.

Information displays: once set up, each sensor's data appears under the WATER menu, reading in 1% steps rather than the 25% steps a rod/stud sensor uses. The EC940's 4" display shows fresh and waste levels on separate screens (use '>' to switch), while the EC970's 7" display shows both together on one screen.

To link a Webasto Thermo Top EVO heater to the Sargent MC100 Control Unit (for control via the EC970 panel), you'll need two extra Sargent parts: the Fan Adaptor PCB (17464) and Fan PCB harness (89003-24). Wire it up following the diagram for the Webasto-to-Sargent connections - note that harness cable colours in the standard Modular System kit (K970A) may differ on OEM installations.

For setup help with the heater itself, contact Webasto directly or check their portal at https://my.webasto.net/en/. On the Sargent side, enable the Webasto Thermo Top from the ADVANCED SETUP menu first, which then adds a 'Heating' option to the home screen for controlling it - the Help button in the top-right corner explains each individual control.

If you're technically minded, yes - each Heat Air kit includes a detailed step-by-step installation guide. Otherwise, a local motorhome workshop should be able to fit it for you. Whoever fits it, a qualified gas engineer has to certify any gas work to BS EN 1949-2011.

The models differ in heat output and fuel type, with options for both campervans and panel-van conversions - broadly, the bigger the vehicle, the more output you'll want. Gas-only suits off-grid touring; if you mostly stay on sites with hook-up, the gas-and-electric version adds 3kW of electric heating.

Yes. Every Heat Air model can run on gas, and on its low gas setting it draws very little from the battery - as little as 0.6 A.

Take the waste-holding tank out through the service door, stand it up so the pour-out spout faces upward, then take the cap off. Add the recommended amount of Thetford waste-holding tank additive plus roughly 3 litres of water so the bottom is covered, refit the cap, and slot the tank back into place.

Pull the safety catch upward to release the waste-holding tank, then slide it out, tipping it slightly as it comes free. Stand it upright with the emptying spout facing up, unscrew the cap, and pour in the recommended amount of Thetford toilet fluid plus about 2 litres of water to cover the base. Screw the cap back on, return the spout to its stored position, then slot the tank back in through the access door and re-secure the safety catch.

The warning light comes on once the tank holds more than about 15 litres, leaving roughly 2 litres of spare capacity - good for around 5 more flushes. Empty it as soon as the light shows rather than letting it get any fuller.

With the valve blade closed, open the outside access door, pull up the safety catch and take the tank out. Carry it by its handles to a toilet or legal waste point, stand it upright with the emptying spout facing up, and take the cap off. Hold the tank by its upper handle, and once the spout is pointing down, use your thumb on the rear handle to hold the vent plunger in so it drains without splashing.

Once it's empty, flush it through and rinse the valve blade with water before sliding the tank back in and locking the door.

Yes, as long as it's in a heated part of the vehicle - otherwise there's a risk of the water inside freezing. If it isn't heated, drain the toilet the same way you would for storage: empty the flush water system and the waste tank, and leave the cap off the emptying spout so the tank can dry out.

Give the waste tank seal, the cap seal and the pressure-release vent seal a regular clean with Thetford Bathroom Cleaner - once a month is usually plenty if you're using the toilet often. Avoid household bleach, solvents or other harsh cleaners, as these can permanently damage the seals. Not using the toilet for a while?

Clean the seals and add a light coat of Thetford Seal Lubricant to keep them supple - Vaseline or vegetable oil will cause leaks, so steer clear of those. The valve blade's seal wears with use, so however well it's looked after, it'll eventually need replacing.

Remove the waste-holding tank via the service door, stand it upright with the pour-out spout facing up, remove the spout cap, add the correct dose of Thetford waste-holding tank additive plus around 3 litres of water so the bottom of the tank is covered, then replace the cap and slide the tank back in. On the C402-C and C402-X, also fill the integrated flush-water tank via the waterfill funnel with the correct dose of Thetford flush-water additive plus clean water.

Open the blade by turning the control knob anticlockwise; it can be left open or closed while the toilet is in use, but should always be closed fully afterwards (turn clockwise until it clicks). To flush, make sure the blade is open and hold the flush button down for several seconds. Don't leave water standing in the bowl when the toilet isn't in use, and don't travel with water in the bowl - both risk water damage to the vehicle.

Pull the tank's handle up until fully extended and remove it via the service door, take it to an authorised waste disposal point, stand it upright with the pour-out spout up, remove the cap, then hold the vent button in while emptying so it doesn't splash. Add around 5 litres of water, replace the cap, shake gently to clean the inside, then empty it again before sliding it back into the toilet.

It needs emptying once the tank's red level indicator lights up - at that point it can only be used for two more flushes, and shouldn't be travelled with when more than three-quarters full.

Place a bowl under the drain tube, pull the tube out to let the remaining water drain into it, then close the tube and put it back. Only do this if the toilet won't be used for a while - Thetford recommends travelling with the flush-water tank empty, or at most half full, to avoid water damage.

It's fine to use in cold weather as long as it's kept in a heated part of the vehicle - otherwise there's a risk of the water freezing. If it won't be heated, or before long-term storage, fully drain the toilet and the vehicle's water system: empty the flush-water tank (where fitted) and the waste-holding tank, clean and dry the whole toilet, then open the blade and loosen the pour-out spout cap to ventilate the waste-holding tank.

Open the fresh water tank's drain valve, then the wastewater tank's (into a suitable container), then leave every tap inside the vehicle open (mixer taps set to their central position). There's also an internal drain valve that clears the water heater and its own pipework - open that too, give the vehicle five minutes to finish draining, then briefly run the pump to clear any water left in it. Empty the cassette toilet too.

Yes, product code is WX1599.