I hope this is the right place for this question, since it’s about power...

There are LOTS of tutorials for DIY battery charge indicators, but that’s not what I need. I have a stupid beard trimmer that doesn’t indicate its charging status — not even a flashing light. It doesn’t even indicate when it’s fully charged.

FWIW, I have limited electronics experience, all Arduino. But this seems like it might be a simple circuit...? I’m perfectly comfortable splicing something into the charging cord, if that will let me do what I want. If I have to cut into the trimmer to get to a circuit board, that’s probably more than I’m willing to do. Probably.

Does anyone want to hold my hand through this project, or can you point me to a tutorial that would work, or maybe just help me modify an existing one?

Thanks in advance!

 

It's actually not that simple to indicate charge status of most batteries.
Often a dedicated IC is used that actually monitors the input and output total charge transfer to determine the battery charge status.

First step is to determine what type of battery the trimmer has.

 

One simple way to know the status of battery charge is to monitor the battery current.
The trimmer will have a charger unit that takes care of the charging process.
If the charging current is Above a Threshold, the battery is under charging state, if below that threshold, it's charged.
Use a Hall Effect Current Monitor to monitor the battery current.

You will need to "implant" a Hall Measurement unit inside your Trimmer and take 3 monitoring lines - Gnd, Sense and Vcc.

 

Okay! Will one or the other of these get me started?

https://www.sparkfun.com/products/11005
https://www.sparkfun.com/products/13679

 

https://www.sparkfun.com/products/13679

This is the one I referred to. Its a 5 Amps Unit. Should suffice for your needs.

 

The second one is best ,13679/ red pcb...