From bigclivedotcom.
These devices are actually very useful, but they have a huge problem. If used with some prominent brand power tool batteries they can over discharge them and potentially cause their chargers to reject them.
There are two common approaches for battery discharge monitoring in power tools. Having the overdischarge circuitry in the battery itself or having it as part of the powertool control circuitry.
DeWalt and many other prominent brands do not have active batteries, possibly to avoid the need for high power transistors in them. But many of the clone tools do have active overcharge and overdischarge protection. Ryobi also have the in-battery protection to maintain their backwards compatibility with older tools.
If used with suitable batteries these units are very useful though. They do put out a decent current at 5V on the two parallel USB sockets. They also go into a sleep mode if there is no load connected, but it doesn’t take much current to keep them awake.
The 1.5mA quiescent current might not seem much, but it is significant over time, especially with a battery that already has low charge and is for a specialist tool that doesn’t get used much. So make sure you don’t leave the module plugged onto a battery.
Here’s a link to the one that works with knock-off Makita batteries:-
https://www.aliexpress.com/item/1005006898931307.html
Shop about and they will probably appear at a low price.
If you have accidentally overdischarged a battery then it may be possible to recover it by bringing the cells (or pairs of parallel cells) back up to 3V each at low current. But if the cell voltage has gone too low or worse still is showing reverse polarity, then do not attempt to recover them, as power tool batteries see high stresses in normal use.
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