Battery capacity
The electrical capacity of a battery, in other words, the amount of energy stored by a battery when fully charged. The capacity value is expressed in amp-hours and indicates the number of hours during which a fully charged battery will be discharged to the minimum allowable charge, delivering a current of 1 ampere to the load. For example, a capacity of 40 Ah means that the battery is capable of delivering a current of 1 A for 40 hours, or 2 A for 20 hours, etc. In fact, a more capacious battery gives more attempts to start the engine, and is also able to work longer at a low load (for example, when powering a car audio system).
The capacity requirements for different transport types differ markedly. So, in motorcycle batteries, it rarely exceeds 20 Ah, the average value for passenger cars is 40-80 Ah (but there are options for 100 Ah or more), and for heavy equipment like buses, an acceptable capacity starts somewhere from 100 Ah. The optimal value of the battery capacity is often indicated by the manufacturer in the characteristics of the vehicle, and when choosing a model by capacity, you should focus primarily on these figures.
Starting power (EN)
Battery starting current measured in accordance with EN (Uniform European Standard). According to this standard, the starting current is the maximum current that a battery at an electrolyte temperature of -18 °C can produce for 30 seconds without a voltage drop below a certain level (for standard 12 V batteries — not lower than 7.2 V). The term "starting" appeared because this mode of operation is similar to starting the engine, when the battery has to supply a high power current to the starter for a short time.
The recommended value of the starting current is generally related to the weight category of the machine: the heavier it is, the more powerful current is usually needed to start. And many manufacturers directly indicate the recommended values \u200b\u200bin the characteristics of a particular model of transport. If the battery is bought as a replacement, then the general rule is that its starting current must be no less than that of its predecessor.
Note that in fact there may be designations of starting current according to 3 more standards: SAE (USA), DIN (Germany) and TU (GOST 959-91, Russia). The first one is practically identical to EN, while DIN and TU are quite easy to convert to EN and vice versa: they are similar to each other, and each of them gives a number approximately 1.7 times less than NE. That is, for example, to replace a battery with 200 A according to specifications, you should look for a model with a current of at least 340...A (200 * 1.7) according to EN.
