Battery monitoring - State of Charge, Discharge floor, Time remaining etc. We sort out the concepts!

Digital Skipper |11/11, 2021

Batteries have a number of different uses, mainly to store energy for later use. But how much energy is stored in the battery? It is not possible to determine this by just looking at; the battery. The lifespan of batteries depends on many factors. Battery life can be shortened by undercharging, overcharging, excessively deep discharges, excessive charge or discharge current, and high ambient temperature.

Whether you have a boat, mobile home, caravan or an off-grid accommodation ömonitoring the battery with an advanced batteryömonitor important soå that corrective actions can be taken if necessary. This extends the life of the battery and the battery monitor quickly pays for itself.

Installation is usually simple and builds regardless of which manufacturer you choose; the same principle, namely that you let the current pass through a "shunt" which, together with the battery type and capacity, makes it possible to calculate the remaining capacity, time, etc.

Some of the most common terms around battery monitoring are; State of charge, Time remaining, Discharge floor and State of Charge alarm and the world would be simple if these terms had the same meaning for all manufacturers, but only This is not the case and here we will clarify the concepts for Victron Energy and Simarine.

State of charge
Ä is a % value to which the battery is currently charged.

Time remaining
Äis the time remaining before the battery discharged.

Discharge floor
A % value for how far the battery can be discharged before it harmful. For a lead battery it is usually 50% and for a lithium 90-99%. For example, a 110AH lead battery with a Discharge floor på 50% 55Ah available capacity.

State of Charge alarm
Ä a % value for charge level; which triggers the alarm.

The table below shows how Victron Energy and Simarine handle these values and if you have a battery meter from another manufacturer, just look in the manual for ;r to see how your particular product handles this.

Size / Manufacturer	Victron Energy	< br>	Simarine
State of charge	Always displays 0-100% no matter what "Discharge floor" is set to, which means that it is not possible to make a direct comparison with "Time remaining" which shows time to "Discharge floor".		Shows charge levelå with regard to the "Discharge floor" which means that a lead bank on 100Ah with "Discharge floor" onå 50% and a discharge onå 25Ah gives "State of Charge" på 50%.
Time remaining	Shows the time until the set value for "Discharge floor" which means that it is not possible to make a direct comparison with "State of Charge" showing 0-100%.		Displays the time remaining until the set value for "Discharge floor" and in Simarine's case it is possible to make a comparison with "State of Charge".
Discharge floor	Add the value appropriate for the current battery.		Add the value that suits the current battery.
State of Charge alarm	Added to the value of "State of charge" not necessarily with regard to "Discharge floor" where the alarm should be activated.		Added to the value of "State of charge" which at Simarine takes into account the "Discharge floor" where the alarm should be activated.

For trimming your battery monitoring, we recommend that you also look at our post about Peukert's exponent.