but do I need a special circuit in order to cut-off the power once it battery reaches a certain level?
...because a single cell (3.7) wouldn't be able to power the Arduino (5V)..
Quotebut do I need a special circuit in order to cut-off the power once it battery reaches a certain level?This is usually handled by the charging chip but when you buy batteries from a reputable source, they usually ask if you want a 'PCB' (protection circuit) embedded in the battery.
This is a tiny board bundled in the outer sheath of the battery that you cannot see and does not materially change the length of the battery.These boards help preventing over discharge, short circuit protection and sometimes overcharge protection.https://master-instruments.com.au/related_info/PCMs%20for%20Lithium%20Ion/PCMs%20MI%20Offer%20for%20Lithium%20Ion%20and%20Lithium%20Polymer%20batteries.htm
When the voltage and/or current return to acceptable levels, the safety circuit automatically resets allowing normal operation of battery assembly.
If you want to stick to Li Ion then your will probably end up with the 18650 format cell (in link above) unless you go for a proprietary format/charger such as camera batteries. If so you will need a holder such as these:http://www.digikey.com/product-detail/en/BK-18650-PC4/BK-18650-PC4-ND/2330513This will allow you to remove the batteries and charge them individually if you want. (Be sure of both batteries getting full charge).
LiPo is useful if you need high current. If not, NiMH may work better. But, if you feel you must use LiPo, I would suggest you use LiFePo4 as it's the latest technology and doesn't have the "explode" factor that standard LiPo does. LiFePo4 are readily available outside the US (as most are made in China and HK). Anyway, they have a little lower voltage (3.7/3.3 per cell) but that actually works out well for battery powered systems.As far as charging. It's fairly straight-forward. I typically do a trickle charge via solar with a voltage limiter with a simple voltage devider. This works with any type of LiPo battery. If you go with a trickle charge and voltage limit, the main thing to worry about is low voltage. You need to devise a circuit that will terminate when the voltage is lower than a certain amount. If not, you'll kill your LiPo battery.Tim
Is it safe to assume the camera batteries I linked to have this protection circuit embedded?
..maybe I haven't made myself clear, I don't need help charging...
...but I got confused with your comment "bundled in the outer sheath of the battery...
Does it mean the Arduino would stop functioning just as if I had removed the battery
I don't really feel like using 18650s since they seem a bit untrustable.