I have a couple of Kgo batteries. At 17 each they are okay. Though I would suggest if you want a back battery you might want to go with the ego style variable voltage battery passthrough. The 650 mah one is like $15-17 and the 1100 mah is around $20. You can use it as a passthrough when you are near an outlet with a usb charger plug, (get a 2 amp one) or computer (which I found on a desktop it works fine if you have a power source of 800watts or more.) I wouldn't suggest plugging passthrough into laptops though, the power source wattage on most laptops (save for ibuypower gaming laptops or Alienware ones) are much lower than that.
I've got the ego passthrough and a simple 5v joye 510 stick passthrough for when I'm at home and need a backup. I also keep a usb car charger in my car as well to use the passthroughs. There is also an
ego vv passthrough that is just a dedicated passthrough without a battery for $15 too.
But with all the chunky batteries (non mod batteries) they do have a life span that might be 3 months, might be 2 years, depending on what you use on it and how often you use it. The kgo and egos work better with single coil cartos, and work well with standard res attys, like 2.0-2.3 ohm. With the single coil cartos and a tank, I like the 1.7 ohm punched single coil cartos, though 1.7 and 1.5 dual coil cartos do work on them, but the don't vape quite as well. Single coil boges or smoktech cartos at 2.0 ohm works well on them too. Though on my ego passthrough at 4.2 volts I can run 2.0 dual coil cartos that vape ......ed amounts of vapor from them and seem to last about 3 weeks for a carto on a single flavor (I avoid cleaning cartos for flavor purposes anymore.)
If you're going to get another mod, really look around and decide what type of button you'd like and what voltage you want to vape at and how much you want to spend...also your lifestyle. You might want something with a tank and a carto, or a CE2 or 3 or 4 style carto because you don't want to be filling up constantly, or you might like dripping in a 306 or 510 at home and use a tank while you're outside the house, or you might like the taste of a type of carto with a specific juice...(especially after a few weeks of not smoking when your sense of smell and taste are no longer polluted.)
Don't go for a Silver Bullet just cause all the cool kids have one. lol If you really like the shape of it, the button placement and the voltage is right for you, then go for it, but it really is all about personal preference. There are sooo many mods out there now, and it's fun to just have cool ones, but if you don't have a ton of money to spend on it, you want to get the most bang for your buck, so look around before you invest.
I know personally, my next mod is a lava tube style, because I like the variable voltage.