1st time electronics project

Good afternoon people, this is my first post on this forum and I'm looking for some advice.

I am currently designing a nightlight intended for outdoor use all year round, however it will run off battery therefore making it portable for camping trips.

in total, the product will contain 21 ultra bright leds, 7 emitting white, 7 blue, 7 red . . . however i am completely stuck as to what battery to select to run this product. initially i was thinking a 9volt lith ion however i have a feeling it won't be strong enough to light up a certain area at night, are there any batteries you would recommend for a circuit like this? the body will be plastic, so obviously i can't have it giving off to much heat either.

when it comes to batteries i am completely clueless, however i do need it to run for approx 50 hours (allows for roughly a weeks camping)

many thanks

You have to determine the current consumption of your circuit before you can value a battery for it. How much current total does the entire circuit draw when it's powered and how are the LED's regulated? This will of course depend on how you have the LED's configured, and whatever else might be drawing power in the circuit.

Lithium batteries are 3.4volts nominal per cell so 3 in series would actually be 10.2 volts (Approximately 9.3 volts near full discharge and 12.3 maximum when fully charged) your circuit has to compensate for the voltage drop or you'l lose light ouput towards the end, this may be acceptable as it's only a camping light.

If you can post the current draw of your circuit it's basic math to work out the pack capacity required. Model aircraft/car Lithium batteries and chargers are available in quiet large sizes and are very reasonably priced now.