You're probably a lot more electrically inclined that I am. Yeah, I've heard of people doing that. I think it's best to use a 12v charger because charging 4 cells at a time is better because you get less variance between the cells. Keeps the cells more balanced that way.

One more thing, if you plan on getting the black and decker 12v charger, the alligator clips were too big to put on the terminal bolts. The bolts were too low and the top case was interfering with getting the clips on. It was a minor problem and I fixed it by putting a nut on the bolts so that they would sit higher up. I like that black and decker charger because it tapers off the current once it gets close to full charge. It will automatically select the right charge setting but I manually use the "Gel" and either a 2 or 10 amp charge depending on how depleted the battery is.

BTW, the watt meter connects to the entire battery pack so you'll connect it to the full 36v pack. So when you hook up the watt meter, it'll probably say something like 42v or 41.7v and the reason we use a watt meter is because when it gets around 36v, that's when you enter danger zone and need to stop using the battery. Because at 36v, that means each cell is around 12 cells x 3.0 = 36v ...each cell is around 3.0 v . The cells cannot go below around 2.5v . You only need to know about it. I don't really even look at the watt meter anymore because I know roughly how far it can go and I check it every maybe 30 min just to see how depleted the battery is. It's more about how depleted the battery is more than how low the voltage is. You've only got a 20 or 25 amp controller so you are well below the maximum C rating for the battery.