We installed our Lithium Ferro Phosphate (LFP) battery bank in August 2021 (Out with the Old, in with the New). It consists of 10 Battleborn GC2 12V-100 Ah batteries arranged as two serial banks of five paralleled batteries giving us 500 Ah at 24V. We also installed a Victron Cerbo to help control and monitor our Victron equipment (chargers and battery monitor). I subsequently installed a Raspberry Pi single board computer running Signal K to record and display data being generated on board (Boat Data).
I’ve now been collecting the data for three years and I haven’t been doing much more than displaying real time data while on board. As a winter project, I’ve tried to organize and analyze it more carefully.
While at the dock and connected to shorepower, the batteries are not doing very much. The AC needs of the boat (e.g., water heater, toaster oven) are supplied directly from the shore (mediated through the isolation transformer and inverter/charger). The DC needs (e,g, refrigerator, lights) are handled by batteries working with the DC charger half of the inverter/charger. While actively cruising and underway, the alternator driven by the propulsion engine provides the current for DC loads while the AC loads are taken care of by inverter part of the inverter/charger powered through the alternator.
It is only while at anchor (or occasionally at a dock), with no shore power connection, that the batteries must do work and discharge some of their stored power. In the three cruising seasons for which I have data (2023, 2024 and 2025), I identified 247 depletions of significance. I ignored the small discharges that occur when transitioning from shore power to engine power when leaving the dock, and the reverse situation, engine power to shore power, when arriving at a dock. I also ignored short duration discharges associated with events where the engine is off and you aren’t on shore power (e.g., visiting a fuel dock, waiting in a temporary anchorage for currents to subside).
The first chart shows the distribution by duration of the 247 discharge cycles. Our cruising style is one of motion and we only spend multiple nights at anchor in one spot a dozen or so times a year. When we do, we run our generator daily to recharge the battery banks. A lot of the 20+ hour discharge cycles are probably associated with multiple nights at one site. Being a slow boat, cruising around 6-1/2 to 7 knots, we tend to put in long days to cover the same distance that faster boats do. The short duration discharge cycles often represent a 7 PM arrival at a destination followed by a 5 AM departure the next morning.
The next chart shows depth of discharge (as measured in amp-hours, Ah) distribution for those same 247 discharge cycles. The same comments as above about deeper discharges being associated with multiple nights at anchor and smaller discharges representing longer days underway apply to the distribution.
The last chart shows the power consumed by hour of the day. There are certain items on board that once they are turned on are rarely turned off. The big examples are refrigerators and freezers (we have two of each) and all our monitoring equipment (e.g., the NMEA2000 bus).
The data show that we consume 8-9 amps as a baseline. Because we are primarily operating on DC, while at anchor, we tend to turn on the AC inverter part of the Inverter/Charger only when we need it (e.g., using the Starlink antenna). Turning on the inverter tends to increase our usage by an additional 4 amps (we rarely use the inverter to run a large AC load like a toaster oven or electric kettle).
The last major DC load is the Kabola furnace. On cold mornings, we often heat the boat up with the Kabola. It will easily use 8 amps as the pumps and blowers kick on but after things warm up, the load usually drops to around 4 amps. There is a temperature dependence to our usage. Cold weather will result in longer and more frequent operation of the Kabola while hot weather causes higher duty cycles in our refrigerators and freezers. The highest usage is in the early evening when we would have AC power on in order to watch streaming TV via the Starlink antenna and set the Kabola thermostat up to keep the boat comfortable.
When comparing our amp or amp-hour numbers, remember that we are operating at 24v DC. The equivalent numbers for a 12v DC system would be double.
