Hello All

I would like some insight into battery capacity.

Driving an Arduino and 3x 8x8 LED Segment Displays.
Putting this on a bench PSU shows it is pulling 0.22A at 9V.
At 5V pulling 0.12A it still works perfect.
The Arduino and the displays goes off at 4.8V.

I need to get a cheap rechargeable battery that can run this circuit as it will be charged with solar power.
Lets say I get a small 9V 650mah battery. It will drain within 3 Hours, but where will the battery voltage levels be? Would the battery still power the device? Any insight please? Also what battery would you guys recommend?

Regards

 

In theory that the voltage of battery will be down to 0V, because no current no voltage.

You can choose Li 18650 battery, it's easy to buy the battery and battery charger, if you want to use solar power, you also could buy one or show the V/I infos of solar power, maybe could give you some suggestion, but if you don't have too much experience to DIY, maybe buy one is better.

 

Scottwang

I am checking out the batteries and they look really good for what I need to do with them. Adding 2 of them in series gives 3.7V x2 = 7.4V which should be fine to power it up as well as the current which goes from 2500mah to 3600mah per battery. The current stays at lets say 2500mah if adding the two batteries in series right?

 

You can in series for same current or in parallel for double current.

I bought a new box for battery bank and some second hand 18650 battery which dissembly from laptop and they were working fine.

 

I need to get a cheap rechargeable battery that can run this circuit as it will be charged with solar power.

You probably want to go with NiMH; AA batteries will be least expensive. Put them in parallel and series until you get the current and voltage you need. AA NiMH at 1.2V @ 2.5AH at common these days.

Lets say I get a small 9V 650mah battery.

This is a non-standard battery.

It will drain within 3 Hours, but where will the battery voltage levels be?

Your circuit will stop operating at 4.8V. To determine how long it will take your battery to get there, you need discharge specs for the one you select or you need to run tests to determine on your own.

You don't mention how complex you want your charging circuit to be. If you're just going to charge from a solar array, you'll likely affect battery lifetime.

 

What sometimes help visualize how a battery's voltage varies as it discharges is to look at that battery's discharge curve or a family of curves such as that below. Most if not every battery and cell manufacturer publishes these curves. Google is your friend.