I have a project in mind with Arduino but I wanted to use a battery to power all of it. I have to power a Wi-Fi module and a small servo/stepper for a short period of time, maybe a RTC circuit and a few leds/buttons.
It's something that I will use extensively, so changing battery everytime would be expensive and boring. For those reasons I want to implement a charging solution for my device.
To power it, I've discovered this 9V Li-ion battery (http://anrieff.net/batterytest/details/others/e3-LiIon-9V-en.html), which seems great. The writer claims:
Protection circuit: This battery is not a "pure" 2-cell one; it has a protection circuit. It switches off the battery out of the way when the internal voltage drops below about 6.1V. There's an upper limit as well (or so they claim), but I haven't tested it, it should be around 8.5V.
Li-ion are charged at 8.4V (2 × 4.2V).
So, if I understand well, I need to charge it at 8.4V. My questions are:
- I have one of those multi-voltage power supply, which can power 5V or 9V. Can I use a step-down circuit to transform 9V to 8.4V? Charging it with 5V will extend the charging time but charge it in the end?
- 1A (max) power supply will work well?
- Do I need extra special measures, like some protection circuit I'm unaware of?.
- How do I know when to stop charging?