Which Victron SmartShunt size do I need for a lithium battery on my pontoon boat?
For most pontoons, the 500 amp SmartShunt. The 500, 1000 and 2000 amp ratings are the maximum continuous current the shunt can carry, not a measure of how precise it is. Pick the one that exceeds the largest current the bank will ever see.
| Your pontoon's bank feeds | Shunt |
|---|---|
| Trolling motor, livewell pump, stereo, fish finder, lights | 500 A |
| A large inverter, an electric outboard, or a high-draw trolling motor on 24 or 36 volts | 1000 A |
A trolling motor draws tens of amps and the accessories a few more, so 500 amps leaves room to add an inverter later. Owners sometimes ask about a smaller 300 amp unit for a trolling bank; the logic is the same, and the 500 has the headroom.
Why lithium needs a shunt at all
Lithium voltage barely moves across most of its capacity, so "12.9 volts" tells you almost nothing about when to head in. The shunt counts every amp in and out and shows state of charge and time remaining on your phone.
The wiring rule that decides whether it reads right
Every negative on the boat goes to the load side of the shunt. Nothing else touches the battery negative post. Pontoons collect stray grounds over the years: a fish finder wired straight to the battery, the trolling motor's own ground, an onboard charger, a bilge pump. Any of those bypassing the shunt makes the reading drift from day one. Run one cable from the shunt to a busbar and land every boat negative there.
Where to mount it
- As close to the battery as the cable allows, so the battery-to-shunt negative run is short.
- High on a bulkhead, dry and above any water in the compartment. It is not rated for immersion.
- Within Bluetooth reach. Aluminium decks and metal battery boxes cut the signal, so you may need to stand near it rather than read it at the helm.
Set it up for lithium
Enter the bank's capacity in amp-hours, set charged voltage just below your charger's absorption voltage (use your battery maker's figure), and set Peukert to about 1.05 and charge efficiency to about 99 percent. Charge fully and sync to 100 percent once.
If the outboard charges the house bank, a DC-DC charger such as the Orion XS limits what the lithium can pull from a small engine charging system. Protect the trolling and accessory circuits with a waterproof resettable breaker like the 200 amp DC breaker, and fit a lithium-rated fuse at the battery positive.
What you need
Want the full walkthrough? Read the complete guide.