should i let my battery run low once in a while ?

Yes, though do not let it run completely out.  And you should have the option to limit the charge to 70-80%, which is a good idea if the system is run on AC power most or all of the time.

@ejn63​ thank you ,   ive done that in the custom settings.  but what should i set it to for the "start charging at" % ?  im currently on 71 and its plugged in now but not charging because the default to begin charging was set to 50 %

@icantchooseone​ The widely accepted answer for storage of a Li battery is the best state of charge is 50%.  Since the battery is basically in storage when you're using the Dell power control app and the laptop is plugged in, leaving it at 50% would be good.  In the app the lowest setting it offered on my wife's laptop was 50% for when to start charging.  We have the max set to 80%.  Wish I could get an app for my phone that would work that way and just shut off charging at a specified percentage, all I've found is just an alarm that you can set to tell you when you've reached a certain charge percent.  If you're not around to take it off the charger, it still goes to 100%, which is not good for the life of the battery.

@gcraig0001​ someone told me this : The easiest is just to set it to the default setting mainly on ac power/plugged in. Then the system will manage it and never fully charge the battery. ??? 

I set mine to "Primarily AC Use" and the defaults were 50 and 90. Unfortunately it continues to charge to 100 %. Will have to investigate the fix; if anyone has an idea please share. Thanks.

@icantchooseone​ I prefer to choose my own settings instead of automatic, thus I used the custom option.  I think the "mainly on ac power/plugged in" option uses 50% to start charging, but I'm not sure what the system automatically sets the maximum to.  Studies have shown the best max charge level to maximize battery life should be 80%.  See if your automatic setting will let you change the maximum charge and set it where you want it.  As to your original question, if you rarely or never use the laptop on battery, there is no reason to charge it beyond 50%, and there is no advantage to running it down and charging it every one in a while.  Each discharge and recharge cycle reduces the life of the battery by a tiny amount.  Letting it stay at 50% all the time doesn't create a discharge/recharge cycle, and it doesn't degrade the battery.  My wife uses her laptop like a desktop, it never goes anywhere.  

@Maxd1​ Try using the custom setting and set the maximum to 80 or 90, whatever your preference.  See if it works on that setting instead of the automatic one.

@Maxd1​ you cannot have both option . 

@gcraig0001​ hi - when you use  "mainly on ac power/plugged in" - it will charge the battery immediately after plugging it to AC even if the battery was at 99% - you cannot customise it .    ive set mine to custom ( 50 to 80 ) and my battery is still on 100 . it would prob take over a year to drop to 50 - if not longer 

@icantchooseone​ Lithium ion batteries have an extremely low self discharge rate, unlike lead acid batteries, so you are correct, as long as your laptop remains plugged in the state of charge of the battery will stay pretty much where it is.  I suggest you unplug and let the battery run down to about 60%, then plug in again.  I've done that, and it doesn't immediately charge the battery but instead waits until it drops to 50%.  That's why I prefer the custom setup versus the automatic setting.

@gcraig0001​  thank you . why not  unplug till it drops to 80 ?  

@icantchooseone​  80% is a good upper limit for a battery in use, but the experts say for storage the optimum state of charge is between 40 and 60%.  That is the point where the internal parts are under the lowest electrochemical  stress.  When we run our laptops almost exclusively on A/C power, the batteries are basically under storage conditions.  Stick to the 50% - 60% range and the battery will last longer.

@gcraig0001​ much appreciated