Motorhome advice: How to fit twin high-capacity batteries

All motorhomes have limited off-grid power capacity, which can leave the owner short of energy, particularly when power-hungry equipment is being used. This is especially true for those of us who want to use additional electrical items via a mains inverter, such as a microwave or a hairdryer.

I often use our Swift Rio for short overnight breaks and find myself requiring use of the microwave or a fast brew with the electric kettle, so I installed a hefty low-frequency, pure sine wave inverter. My inverter calls for significant power demands, typically 100A for several minutes when using the microwave and I need to continue to power everything else, including the lights, television and satellite dish (and the PS4 games console when my son is resident). It was clear I was going to need a battery set-up that provides an excellent high-current performance, uncompromised life.

My Swift Rio was equipped with a solar panel and an excellent but rather heavy and bulky victron AGM lead battery mounted sideways under the driver’s seat. The passenger seat has the same volume beneath, but Fiat has put the spare wheel jack/tool kit here. This can easily be removed (to stow elsewhere in the habitation area), leaving space for a second leisure battery if required.

My previous battery wasn't cheap but it only had a 2 year warranty and I knew that my leisure usage was destroying this battery at a rate of knots because I was often discharging it beyond its safe limit and it was showing signs of reduced capacity after just a year!

I looked at what was available and there’s a bewildering range of battery technologies. The best batteries on paper are undoubtedly lithium iron phosphate (LiFePO4) models but several seemed to need bespoke chargers to work efficiently with Swift’s existing smart charger and solar panel.

Then I stumbled upon a company called KS Energy. They manufacture very high quality lithium leisure battery which has a built in battery management system that allows you to drop them strait in. A like for like swap! Moreover they carry additional capacity (nearly 106Ah) so could provide the full nominal 100Ah capacity using Swifts existing charge! I was sold.

I fitted two 100AH model KS100 batteries sideways under modern Ducato cab seats – it’s uncanny and almost as if they were designed for them. Since they use sealed lithium phosphate technology, there are no safety ventilation and orientation considerations, either. The two batteries only weight 26KG which is not much more than the original battery. The thing is I now have an equivalent onboard capacity of 400Ah compared to loke for like twin 100AH AGM batteries! This is because I can fully discharge them without any damage, whilst an AGM battery cannot go below 50% discharge without shortening its life.

I ordered two of these from an authorised KS Energy supplier (around £700 each including VAT and delivery) to fit under both seats.

I expect to be using the motorhome off-grid at least twice a week, every week. The total cost of this project was under £1400. That’s a tidy sum, but I am safe in the knowledge that I will never run out of power and the set-up should easily last 10 years.

Future planned developments to the present set-up will also include a 60A battery-to-battery charger and some modifications to the original Sargent control box to disable the joint alternator charging, also a solar panel upgrade.

3 Wiring under floor passenger sidejpg

It is critical to ensure the cables are routed in a way where they are free of any obstructions and to rule out possible compression damage during the life of the installation. I used conduit on the outside of the wires to protect against chafing and remember to use grommets if they pass through any panels



5 Wiring underfllor drivers side 1jpg
Fortunately, Swift’s Rio range lends itself to easily pass cables in the voids between cab and habitation floors. This is the passenger side wiring.
On the driver’s side, the battery wires were run from the terminals to the rear of the cab seats (after removing the front and rear seat base trims) underneath the Rio wooden cab floor panel. Be careful not to pinch any existing wiring under these seats as there will be additional wiring present, including the seatbelt sensors and Swift’s pre-existing battery wiring

7 Metal strap loosejpg
When the original Swift leisure battery was removed, I found it was held in place by a metal bracket that hooks to the seat frame. This can easily be modified by shortening the threaded ‘J’ hooks and reforming them in a vice.   Alternatively, both batteries can be strapped in place using cargo ratchet straps. It is vital that both batteries are secured to the underseat chassis and that there is no chance whatsoever of them moving around.
1 Diagram jpg
This diagram shows the wiring options I considered for both batteries linked to my inverter. In my configuration, I used two-gauge (6.5mm diameter) copper wire.

6 Fuse 2jpg
150A safety cut out fuses were added at each positive battery terminal

My experience with KS Energy was in fact so positive that I eventually set-up as the UK distributor and their parent company now design and manufacture the batteries to our bespoke requirements.
Neal Morris