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18650 battery pack question Answered

hello everybody, I need to install (build) a recharging battery pack for my plant shelf.  it will be running an arduino nano, just 3 leds (3mm 20ma each) 1xNTC and 1x water sensor probes (nails).--  no LDR no yellow LED.
I was thinking about getting a 2x 18650 battery holder - I need more battery hours, should we wire the batteries in parallel to get more mAh and boost them 3.7V to 5V. so basically this is what I am trying to custom build to get more hours; DIY Mobile Power Bank Case Kit
I would just buy the mentioned product BUT under specifications>battery it says the capacity range: 1000mAh and below. but the batteries I have are 3.7V @ 5000mAh. does this mean that the remaining 4000 will be lost because the system can't handle it? 
basically what I am asking for is how can I make a long lasting arduino nano powering 18650 battery pack BUT also with a recharging module. these are the items I found that may work together, please remember that I have no electrical experience from before. I have learned everything that I know from instructables, this is a too advanced build for me to figure out without asking a few questions. thank you for your patience, let me know if I have to clear anything out.
batt holder: 
am I even in the right track with this thing? can these be connected together and a switch. again, the goal is max battery life.. maybe add 4x 18650 - 2in parallel + 2in series, 7.4V to arduino Vin, eliminate the booster, even more battery life ?
thank you in advance,

love & peace


There's slightly more to it than that, unfortunately since you are using off the shelf
arduinos, and the USB bus is +5V. You need to change a regulator and a couple of other wires,
but then it will work straight off the battery. A simple USB charging
module should then be fine.

5000mAh will give you roughly 5000/30mA, or about a week of CONSTANT operation. The trick is to NOT be on constantly. Blink the leds very quickly, say 1/4 second every two, and your battery will last 8 X longer - or two months.

3.7V is enough to run an Arduino chip on, and the LEDs, no need to boost it, and lose energy there.

so you are saying I can input a single 18650 3.7V 5000mAh battery to my system as is through the Vin, it will come on and run everything, even the LEDs? I am going to try this, I would also need to purchase less batteries if this is true. I need just the green LED to blink every 5 seconds, the red or blue led comes on only if either sensor is triggered. then the green turns off, and the corresponding (blue/red) led turns on and stays on constantly. this will not happen so often, only if the plant gets thirsty or gets too cold/hot. so the battery usage should already be low. what about the recharging module tho? I need to be able to leave the batteries in while charging, instead of removing them to charge.. just a simple USB charging module. would those work together?