Fast charger on a cheap handheld console - am I slowly cooking the battery or is it a non-issue?

I've opened up a few of these budget handhelds out of curiosity, and the charging hardware inside varies a lot. On my Anbernic clone the charge chip did negotiate properly, so a 65W laptop brick only pulled what the little board was designed for. But I've also had one of the super cheap no-name ones where the board just grabbed as much as it coud, and the battery puffed up within a year of me fast charging it all the time. That one got hot on the back, not just warm, and I ignored it.

So to me the heat question is real, not folklore, but it's a symptom rather than the whole story. Some warmth while charging is normal because charging a lithium cell always generates a bit of heat. What matters is whether it stays warm to the touch or gets to the point where you instinctively pull your hand away. The slow charger keeps the charge rate low, wich is gentler on the cell and generates less heat, so your gut feeling matches what worked out for me. The negotiation side of the argument is only half right. Yes, a well made device asks for what it needs. The catch is that cheap boards sometimes cut corners on both the negotiation and the protection around the battery, so there's less margin for error if anything misbehaves. I keep a small 5W-ish charger on my desk now for exactly this reason. The big brick is for the laptop, not for toys.

I went down this rabbit hole last year with a cheap handheld I use on my commute, and a ten dollar USB power meter from the drugstore aisle settled it for me. Plugged the little thing into my laptop charger with the meter inline and it pulled about the same as it did on the old 5 watt phone cube, just at 9 volts instead of 5. Same watts, less current, so if anything the big brick was easier on the cable. That was one device, but it matched what the spec says should happen when negotiation works. On the heat question, I think you're reading it a bit backwards. My unit gets warm in the back near the charge port no matter what I plug in, beacuse the little chip converting the input voltage down to what the battery wants is doing the work and dumping the waste as heat right there. A faster charge means more conversion, more warmth. The thing to watch is whether the warm spot spreads to the whole back or the battery area stays noticeably hotter than the rest after it hits full. Mine cools down within a few minutes of hitting 100 percent, and that's been my pass test.

I did have one no-name thing years ago where the meter showed it just sitting there sucking full power past full charge, no taper at all. That one I retired. So I'd say trust the meter more than your hand, and trust a battery that keeps climbing in temperature less than either.

That meter trick is what convinced me too. Put one inline with my handheld and the big brick actually charged it noticeably faster than the old wall cube, it just sat at a higher wattage the whole time. Back panel went from barely warm to what I'd call warm-plus, never hot, but the charge light clicked off way sooner as well. Since I'm usally topping up overnight anyway, speed buys me nothing, so the slow cube stays plugged in by the couch. Only thing I'd add is check what the device itself is rated to accept if the listing even says, that told me more than any forum argument did.

The thing I never see factored in is how much of that warmth is even coming from the battery. On mine the back gets toasty right over the charge circuit, not over the cell itself, so the heat is mostly the little board working harder, not the battery being abused. Feels diferent in the hand but it's not the same thing.

Also, if you're topping up overnight anyway, just charge it slower and call it a day. Heat plus a full battery sitting for hours is the combo that ages these cheap cells fastest, and no charger swap fixes that part.

This is making me feel better about my lazy habits. I only ever charge mine with the little 5 watt cube that came with an old e-reader, and I also turn the thing fully off while it charges. A friend of mine leaves his running on the menu screen while plugged in and the back of his feels way warmer than mine ever does. Is the device being switched on while charging actually part of the heat problem, or does that not really matter?

Update: took the meter advice and grabbed one. Plugged the handheld into the big brick through it and the draw barely moved from what the old cube gave it, so the negotiation thing checks out at least on mine. But now the heat question bugs me. If the warmth is the charge circuit working, is it bad for that little board to sit warm for a couple hours every night, or does it not care?