[EVO 4G General] sidepart:
The guy's right. As an engineer you can't just deal behind the back of the public when you're concerned there might be a problem. Still it's a dev community, so we can't pull the plug on this. It's important for users to know that there could be some serious drawbacks here and to tread carefully if they choose to do so. Granted this disclaimer is usually explained when downloading modifications for your phone, but most people breeze by that these days.

I worked with Li-Ion batteries applied to solar vehicles in college. I don't have a ton of professional experience about them, and granted I was a student at the time. Take what you will from my following wall of text. I don't find anything inaccurate about what's being said here. It is essential that you do not overcharge a cell. Charging to 4.2V on a cell and keeping it there decreases the life cycle of the cell. For an automotive application, or even for a laptop expected to last 3-4 years, you wouldn't apply a principle like this. Now, maybe for a phone that users mostly change out every 2 years or so, this isn't such a big deal. Fine. But there are bigger dangers here. As a responsible design company, HTC shouldn't apply trickle charging to Li-Ion cells. They are fully aware that there are design risks, and it shortens the lifespan of their product. As users with a choice, we can be as irresponsible as we'd like. HOWEVER! We still have to prove that we're not experiencing the other dangers involved with overcharging. These dangers aren't limited to bricking your battery.

Oxidation caused by overcharging releases poisonous fumes (smells kind of like anti-freeze). While there's very little exposure in this application, it's important to note that this is a good reason not to apply it to a larger application. Excessive overcharging causes the battery to "vent with flame". That's the most civil way to describe it, more like it erupts into a bright red fireball. If this does happen to you PLEASE don't pour water on it, get some sand.

If you're not concerned with battery lifecycle then; to me, the only other thing I've found to be concerned about is bringing the battery above 4.2V. So far as I can tell, the trickle charging method (whatever it may be) employed here isn't doing that. An excellent point as brought up earlier in the thread though that we can't be sure how accurate the software we're using to read this voltage is. If it is accurate and the battery stays below or at 4.2V, we should "technically" be ok. What does this mean? Well, technically we should be fine if it doesn't go above 4.2V. I say technically because nobody has any idea what kind of bugs could be thrown at the kernel to make it inadvertently charge ABOVE 4.2V. There's no way to 100% know that some stupid godforsaken combination of events won't trigger a fault. This is why you don't ship a product that operates in a red zone like this.

If I were designing a product for others, I definitely wouldn't be ok with a gamble like this. I'm a user in this case though, and I am comfortable with exposing "technically ok" to myself. I personally am curious to see how a trickle charge application pans out for an application like this since it's highly unrecommended. Feel free to participate for yourself. Just be fully aware of the dangers. If you're not comfortable with it, stick with stock kernels and remind yourself that 10% extra battery life isn't really worth the risk.