Don't be the only one giving 100% In the relationship
Now these numbers may fluctuate given the pitfalls and barriers that tend to hit relationships but that does not mean it should ever deplete heck in all honestly if it dips below 50% you are already giving too much and settling for way less than you deserve ( 50 to 150 is extremely lopsided and a relationship is not a place that *lopsided* should ever prosper). Simply put keep the levels in a relationship as close to 100 to 100 as humanly possible and you will experience a love like no other. Love takes a lot of work and as you first meet the levels will be low but that is why you BUILD together until finally reaching 100%.
Both parties just have to be willing to do the work.