Electronics > Projects, Designs, and Technical Stuff
Hotspot battery getting overcharged
drummerdimitri:
I have a netgear 810s portable hotspot that seems to be overcharging its internal battery.
In the past 3 years of ownership, I had to change the battery twice already and it probably only gets less than 50 cycles during its lifespan since I use it docked in its station (ethernet to desktop) most of the time and only rarely ever use it as a portable hotspot.
The reason for changing the batteries is because they always seem to swell and that gets worse with time so for the sake of safety I keep changing them when that happens.
Last time I took the battery out and measured its voltage, it was reading 4.28V which is quite a bit higher than the 4.2V norm to which Lithium batteries are usually charge to so I'm guessing that the constant overcharging is causing them to bulge.
Now my question is, when I get the battery replaced for the third time now, is there anything I can do so make it stop charging beyond 4.2 V? Maybe a resistor or some nichrome wire to drop the voltage "seen" by the battery?
NiHaoMike:
Can you find the datasheet of the charging chip? I once had a cheap pocket AP with a similar design flaw, plus it had the battery right up against the hot CPU.
As for an easy fix if the chip does not have a documented way to change the voltage, a pair of back to back Schottky diodes in series with the battery would work. Even better is to bypass the diodes with a MOSFET when operating on battery power.
amyk:
You need to check the charger IC/regulator; it may have drifted out of tolerance.
Alternatively, fit a 4.3 or 4.35 volt cell --- 4.28 won't fully charge one, but those can tolerate the voltage safely.
Doctorandus_P:
4.2V is the absolute maximum for (apparently most) Li-Ion chemistries.
For long time storage it's usually recommended to save them half charged.
Also, It used to be that when you go above around 4.1V, the battery lifetime (recharge cycles) start diminishing.
Usually batteries are pushed to (or just over) the maximum for the manufacturer's sake.
They get a bit more charge (10 to 15%) out of the battery for your new gadget, and when the battery dies after several years, they are also happy to sell you a new gadget.
But there are 100's, maybe 1000-s of (slightly) different battery chemistries which makes it difficult to give a general answer.
Peabody:
It may not make any difference, but you might see if there's new firmware for the hotspot.
Since swelling batteries are a safety issue, it might be worth a call to Netgear to see if they'll replace your hotspot. 4.28V is definitely too high, particularly if it continues charging all the time instead of terminating the charging.
In any case, you don't want to be using this thing as is. It could catch fire.
Actually, one option might be to get two batteries, and find a way to charge them using another charger. Then you could switch them out as needed, and never apply charging current to the hotspot itself. I'm not sure how the docking station would fit into this. Is it getting power over Ethernet?
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