By Boat Battery editorial team · 2 minute read · Editorial policy
On the negative, between the bank and everything else on the boat. Without it you are guessing at state of charge, and lithium's flat voltage curve makes guessing useless.
Why lithium voltage is a limited charge indicator
A lead-acid bank tells you its state of charge through its resting voltage. Lithium does not. A LiFePO4 bank sits at about 13.2 V from 90% charge down to 20%, so the voltmeter at your helm reads the same at breakfast on day one and at midnight on day three.
Battery and system sides of the shunt
A shunt-based monitor counts amp-hours in and out. It is the only way to know where you are. Fitted on the negative between the bank and the boat's negative bus, so that every load and every charge source passes through it, including the ones you forget: the bilge pump, the stereo memory, the solar controller's own draw.
Loads and chargers that bypass measurement
The common installation error is leaving one load connected to the battery negative directly, usually the engine start negative or a bilge pump wired before the shunt. Anything on the battery side of the shunt is invisible to the monitor, and your state of charge drifts a little further from the truth each week.
Monitor calibration and synchronisation
Calibrate it once at a full charge, then trust it. Most monitors will resynchronise automatically when they see the charge voltage and current thresholds you set for a full bank.
Related installation planning resources
Use these notes to prepare your own measurements and questions. Check the exact equipment manuals and have the proposed system assessed for your vessel before buying or changing electrical components.
Calculate your boat battery capacity
The house bank calculator takes your loads, your nights on the hook, your solar and your alternator, and returns the bank, the DC-DC charger, the AGM equivalent and the weight you take off the boat.
Open the calculator