I think there are 3 types of mods.
Those with built in batteries, like your ego and the innokin MVP. The MVP is bigger, lasts longer, and allows you to vary the voltage or power (VV/VW) to adjust the vapor you get.
The next two take batteries, most commonly 18nnn (were 18 is the diameter, or circumfrence I never can remember, and nnn is the length usually 350 500 650 i.e. 18350) They are lithium ion and are rechargable and most rechargers will accept any of them. When the battery runs down take it out and replace it. You can cary spares around if you need more than one to make it through the day. Be careful cause if it is in your pocket and shorts out it can cause problems, they make little plastic cases.
Regulated mods, like the Vamo, have built in electronics. These serve to keep you from hurting yourself and change how the attomizer, the thing you put the juice in, works. The keep you safe by not allowing you to put a coil with too low an impedance, the battery might explode. They also stop when the battery is discharged, you could continue using the battery, see below, but that will damage the battery and it will not hold a charge as well so it hurts your wallet. They are also VV/VW so you can adjust the vapor.
Mechanical mods, like the Nemesis, are noting more than a tube to hold the battery with a switch. You can hurt yourself with these. Some think they look cooler, they do, and some people like to build their own atomizer coils with resistance under an Ohm, to blow huge clouds of vapor, regulated mods save you from doing this. You can also damage the battery by discharging it too far.