The rule with Li-ion batteries is to keep them 50 percent or more most of the time. When it drops below 50 percent top it up a little if you can. A little a few times a day seems to be the optimum to aim for.
But don’t charge it all the way to 100 percent . It won’t be fatal to your battery if you do a full recharge – most of us are forced to do this every now and again in emergencies. But constantly doing a full recharge will shorten the battery’s lifespan.
So a good range to aim for when charging a Li-ion battery is from about 40- to 80 percent in one go. Try not to let the battery drop below 20 percent.