Suitable battery power supply for my project?

Hey guys, my first post on this forum. I bought an arduino uno a couple of months ago and i am hooked. I have been doing a lot of reading and have some basic knowledge from when i was messing around with electronic kits from radio shack as a kid. I have a project that i am developing and need some advice on powering it suitably via battery. It is basically a 360 degree sensing system that will trigger 120 rgbw neopixels on a strip and also trigger sound effects when someone comes within 1.5 metres of it. I need it to last a full eight hours but it will only trigger lights and sound at full volume/brightness for 5 seconds each time it senses someone. The rest of the time it will lay idle. I dont know how many times it will potentially get triggered per 8 hours so i thought i would just play it safe and was thinking of supplying it enough power to last in a constantly on state just to be safe. My initial thoughts were a 12 volt sealed lead acid battery 7500mh so i can recharge it overnight for use again the next day. Unfortunately i have been doing all my work from home and have not developed any knowledge on how to power my projects via battery. I have an arduino mega powering an mp3 player/amp shield from adafruit with two 3 watt 4 ohm speakers and two metres of neopixel rgbw strip. Could somebody with some knowledge in this area please give me some guidance? I have attached a wiring diagram for reference but please ignore the battery type. Thanks in advance.

I dont know how many times it will potentially get triggered per 8 hours

Well, don't expect anybody else to know so, in the light of that, a decent 12 lead acid is a pretty good idea, particularly if you already own it. Your picture is pretty crude but, if that green thing under "Pack" was a decent 5v regulator and thereby connected directly to the 5v lines it would be helpful. The Mega's regulators are pretty inefficient even when supplied with 9v, and 12v is just making a bad situation worse. This could assume some importance when using batteries. Further, I have no idea of what the power requirements of all those sensors and LEDs might be and I'm sure you can check that, but it wouldn't surprise me if you were stretching the friendship on Arduinos 5v pin, you are certainly making the worse situation worse still, and running them off the abovementioned 5v supply would fix that.

Powering from battery is not that different to powering from mains supply or USB supply. It's all power.

What voltage do those neopixels require? If 12V it's easy; if 5V you better get a buck converter rather than trying to use a linear regulator to power it all. Much more efficient so saves a lot of power (a linear regulator wastes 7/12th or almost 60% of the power supplied in the form of heat - which you have to deal with, too).

The big problem is that you don't know how often it will be triggered so I'd lean to a worst case scenario meaning "it's triggered all the time".

Thanks for your input guys, yes i don't know how many times it will be potentially triggered and that is why i followed the comment up with i am aiming to calculate the power requured as if it were continuously lit just to be sure. The neopixels are strictly 5 volt and i have 120 of them at up to 80ma per pixel. I do have a 12 volt sla attery lying around but if there is a better rechargeable option i would be happy to run with that.

120 * 80 = 960 mA total, plus the Arduino makes for 1A total current. So forget about a linear regulator - get a buck converter to get your 5V supply.

Overall the 12V battery sounds like a very good starting point, and also sounds like it will simply do the job just fine. You mention it's rated capacity is 7500 mAh, so that would be sufficient for your application even when triggered almost constantly.

Do check your battery for maximum discharge allowed and whether it has any overdischarge protection; you may have to add a simple circuit to monitor the actual voltage and shut down your project when needed.

Thankyou so much for your prompt response and useful advice, i have learnt a lot in a very short time already wvmarie, hopefully as i learn more i will be able to contribute something back to the community. +1 karma your way. You too Nick.

You're welcome, and good luck with the project.