We understand that all this terminology can be a bit confusing at times but once you know how it works it is quite simple. Below we will try to explain what it all means. For calculations we recommend using our Trolling motor tool. On tab 3 of this tool you can calculate Watts, Amps, Voltage and Watt-hours.
The number of volts is the amount of energy given to an electronic circuit. By a circuit we mean, for example, an electronic device. With a 12V device, 12 volts are always “given” from the battery. A battery always has a fixed voltage (e.g. 12, 24, or 36 volts) and a device always works at a certain voltage. For example, a device that works on 12 volts obviously needs a battery that also supplies 12V.
When we talk about amperes (or amps), we are talking about how much electricity “flows” per second. If the number of amps goes up, then current flowing through the device per second also goes up. An electrical device usually works on a fixed voltage, but the amount of amps it draws can vary depending on, for example, the position of your trolling engine (a trolling engine at full throttle draws more amps than in half throttle for instance).
Example 1: Suppose I have a Minn Kota Endura C2 50 LBS that I am running on gear / speed setting 2. The trolling engine runs on 12V and currently draws 15A. I decide to go a little faster and I switch to gear / speed setting 4. The engine still runs on 12V but now pulls 25A. The voltage has remained the same but the number of amps has gone up.
Power is the voltage multiplied by the number of amps, or W = V x A. This is the amount of energy consumed by a device and therefore an indication of how powerful it is. This goes up when the number of amps also goes up.
Example 2: Suppose I have a 24V Minn Kota Terrova 80 LBS bow motor that draws 30 amps. So the power consumption is 24 x 30 = 720W.
Example 3: Suppose I have another Minn Kota Endura C2 50 LBS that I am running in gear / speed setting 2. The engine runs on 12V and draws 15A and thus has a power consumption of 180W (12 x 15). When I switch to gear / speed setting 4, the engine draws 25A and still runs on 12V. The power consumption of the trolling motor is now 300W.
Battery capacity is measured in Ah, or Amp-hours. As the name suggests this means how many amps the battery can deliver in an hour. For example, a 12V lithium battery with a capacity of 100Ah can deliver 100A to a 12-volt device for one hour. The same 100Ah battery could supply power for 4 hours (100/25=4) to a 25 ampere device. If a battery has 12V50, this means that the battery works on 12 Volt and has a capacity of 50Ah. A 24V100 battery works on 24 Volt with a capacity of 100 Ah etc. In practice for lead-acid batteries the nominal capacity (how many Amps hours the battery can deliver according to specifications) differs greatly from the effective capacity (how many Amps the battery can actually deliver during use). We explain how this works in our article discharge and battery capacity.
Example 4: I run my Minn Kota Endura C2 50 LBS in gear / speed setting 2, drawing 15A at 12V. I have a 12 volt battery of 70 ah. My total run time is now 70 / 15 = 4.7 hours. When I switch to gear / speed setting 4 the engine draws 25A. My total runtime is now 70 / 25 = 2.8 hours.
Another way to measure the capacity of the battery is in Watt-hours (Wh). Wh is calculated by multiplying the number of Amps with the battery voltage. For example, a 12V100 (a 12 volt battery with a capacity of 100Ah) has a capacity of 12 x 100 = 1200Wh. A 24V50Ah battery has a capacity of 24 x 50 = 1200Wh. So these batteries have the same capacity, only one works on 12 volts and the other on 24 volts. In practice you will notice that these batteries will be around the same dimensions and weight.
Example 5: I have a 600W trolling motor and a battery with a capacity of 1200Wh. My runtime at full throttle is 2 hours with this battery (1200 / 600 = 2). I do not even need to know how the trolling engine or battery voltage to calculate this (as long as they work at the same voltage obviously).
The attentive reader notes that the runtime of a battery with a device can be calculated in two ways. Either by dividing the number of Amps of the battery by the power draw in A of the trolling motor or by dividing the number of Wh of the battery Wh by the number of W of the trolling engine.
Batteries can be connected together to achieve a higher voltage or higher capacity. This is done by connecting the battery terminals of the batteries with cables.
Connecting in series: higher voltage, equal number of Ah
When we say that we connect batteries in series, we connect the plus terminal of one battery to the minus terminal of another battery. This means that you still have a minus terminal available on one battery and a plus terminal available on the other battery. The electrical device should be connected to these two available battery terminals. If we connect batteries in series, the voltage goes up, and the capacity measured in Ah remains the same.
In the picture above we see two 12V50Ah batteries. As you can see the two batteries are connected in series: the minus and plus terminals are connected together. You have created a 24V50 battery : 24V (due to series connection) with 50Ah capacity (number of Amps remains the same). If we measure the capacity in Watt-hours, the total capacity is now 24 x 50 = 1200 Wh.
Connecting in Parallel: equal voltage, higher number of Amps
When connecting batteries in parallel, we connect the minus terminal of one battery to the minus terminal of the other battery and the plus terminal of one battery to the plus terminal of the other battery. We connect the minus wire of the electrical appliance to one of the minus terminals and the plus wire to the plus terminal of the other battery (see the picture below). The same voltage is now supplied but the number of Amps has increased.
In the picture above, the minus terminals of both batteries are connected and the plus terminals are connected. So the battery is connected in parallel. There is still 12 Volt but the number of Amps has increased from 50 to 100. We have now created a 12V100Ah battery. If we measure the capacity in Watt-hours, the total capacity is now 12 x 100 = 1200 Wh.
So the number of watt-hours always remains the same, whether you connect them in series or parallel.
Attention: always check whether batteries are suitable to connect together. Only connect identical batteries (same type/model, age and charge status) and use cables of the correct thickness and length. We recommend that you do not connect 12 volt Rebelcell batteries in series but instead select a Rebelcell 24 volt battery. Rebelcell 24 volt batteries can be connected in series up to 48V without any problems.
The technical specification for batteries often includes many other terms. Below we will try explain what the most important ones mean.
Voltage: this is the voltage that the battery delivers on average. As explained above, the battery starts with a higher voltage than when it is partially discharged. With this we mean the average of this progression or the nominal voltage.
Chemistry: this indicates what kind of lithium battery technology is used.
C1, C5, C20: this indicates battery capacity when discharged in a certain number of hours. C20= 100Ah means that the battery can deliver 100 ampere hours if it is discharged in 20 hours (with 5A). Lead batteries have a lower capacity if they are discharged faster. For example, a lead-acid battery can deliver 100Ah if it is discharged in 20 hours (C20=100), but if the same battery is discharged in 5 hours it will only deliver 70Ah (C5=70). With Rebelcell batteries it doesn’t matter if you discharge them in 20 hours, 5 hours or 1 hour, they always deliver the same capacity. That is why we always refer to our capacity as Capacity (C1-C20). Read more about this in our article about effective battery capacity.
EqPb: this stands for ‘equivalent lead battery’. By this we mean that this battery can be compared to a lead battery with the indicated capacity when used in combination with an electric motor. Often a lithium battery with a much lower Ah can in practice deliver the same amount as a lead-acid battery with a much higher Ah. In practice, for example, the Rebelcell 12V50 can be compared to a 105Ah semi-traction battery in terms of operating time for an electric motor. This also has everything to do with the usable battery capacity.
Nominal energy: this is the battery capacity measured in watt-hours (see above for explanation).
Maximum continuous discharge: this is the maximum number of amps the battery can continuously deliver. Suppose a battery has a maximum continuous discharge of 30A, then you cannot connect a device that draws more than 30A. The higher the capacity of the battery, the higher the maximum continuous discharge.
Peak discharge (10 milli-sec): this is the maximum number of amps the battery can deliver for 10 milli-seconds. This is always higher than the maximum continuous discharge. Some equipment has a short peak discharge when starting up (so called ‘inrush’ currents). This is for example the case when you go from zero to full throttle in one go with an electric outboard engine. At that moment, the motor requires more amps than the rated maximum for a short time.
Lifespan (#charges) (@80%DoD): this indicates how often you can discharge and recharge the battery up to a certain percentage. For example, if it says “Lifetime (#charges) (@80%DoD): 1500” it means that the battery can be discharged to 80% for 1500 times (i.e. with 20% capacity left). For example, if it says “Lifetime (#charges) (@100%DoD): 1000” then the battery can be fully discharged 1000 times.
Energy density: with this we measure the number of Watt-hours per kilo of battery. Energy density is much higher for lithium batteries than for lead-acid batteries. A high energy density means that you can store more energy in the same space. And this results in a lighter and smaller battery.
Bandwidth voltage: see explanation of the discharge and capacity of batteries. This gives the minimum voltage (at 0%) and the maximum voltage (at 100%) of the battery.
Charge temperature: this gives the minimum and maximum temperature at which a battery can be charged.
Discharge temperature: this indicates the minimum and maximum temperature at which a battery can be discharged.
Storage temperature: This indicates the minimum and maximum temperature at which a battery can be stored safely.
Maximum charge current: This gives the maximum current in A at which the battery can be charged. The higher this number, the faster the battery can be charged (with the right battery charger).
Integrated cell balancing: part of the Battery Management System. The cell balancing feature ensures that the voltage of individual lithium battery cells is equalised, so the cells all have the same charge status / voltage. This is necessary for optimal use and performance of the battery.
Temperature protection: part of the Battery Management System. The battery is switched off when the temperature becomes too high or too low. This is a protection to prevent damage.
Maximum discharge current protection: part of the Battery Management System. The battery is switched off when the power draw of your equipment is higher than is allowed. This is a protection to prevent damage.
Overvoltage protection: part of the Battery Management System. The battery is switched off when the voltage becomes too high and the battery is overcharged. This is a protection to prevent damage.
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