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Battery Physical Characteristics - Physical Size
Size: Physical size matters. A Deep Cycle battery is usually bigger (and heavier) than a car battery. It can be physically sizeable in fact so be sure to do some measuring before your purchase to make sure it’ll fit where you want to put it. And be sure to measure to the top of the posts, or make sure they’re included in the stated measurements, not just the basic core shape.
Increased connector flexibility: Deep Cycle batteries usually have more than two posts or terminals. For instance, your 12 volt car battery has two posts, a positive and a negative. Sometimes they’re on the top, sometimes on the side. Deep Cycle batteries have more; two regular posts/terminals, positive and negative, and two secondary’s, positive and negative, are common.
High end deep cycle batteries can last as long as 15 years, maybe more; lower end more like 5-7 if taken care of.
Other Battery Size Measurements - Volts, Amps, Watts and Batteries
There is another “size” measurement to consider and that is amp (ampere) hours. Battery “size ”, how much energy it can hold, is measured in amp hours. Volts and watts are also involved. They are interconnected.
A volt is the pressure of electricity.
A watt is the amount of electricity.
An amp is the volume of electricity.
Volts – The pressure of electricity.
Deep Cycle batteries used in solar energy systems are usually 12 volt batteries or two 6 volt batteries connected to each other in a specific way providing 12 volts.
A 6 volt battery has 3 single “cells” and a 12 volt battery has 6 single “cells”. The “cells” are connected to each other inside the battery. A battery “cell” consists of two lead plates and a positive plate. A “cell” produces around 2.1 volts each. 2.1 x 6 = 12.6 volts. How many 12 volt batteries you need depends on your use. One 12 volt battery, or 12 volt equivalent (6 volts + 6 volts), can be plenty. Battery voltage can be higher and batteries can also be connected together in different ways for increased pressure/voltage or capacity. (They can collectively become 24 volts or even 48 volts.) It’s just important to know what voltage you’re working with.
Will the 12 volts of pressure go on indefinitely? No. As the battery energy/electricity is used without immediate replacement, the voltage (the amount of electrical pressure) will go down. A battery is considered dead if it goes down to 10.5 volts. It has something to do with its internal chemistry that makes it unrecoverable or close to it.
Inexpensive volt meters can be very helpful. If a battery is discharged down to 20% (an 80% discharge) a volt meter will show around 11.58 volts. Volt wise, batteries actually charge significantly higher than 12 volts. A fully charged battery at rest (3 hours after charging has stopped) will be around 12.7 volts and 13.6 under charge.