What Meta4 said, check the airline's guidelines. While 99% of airlines will allow you to carry batteries on board, total number of batteries you may carry and max capacity of each battery may differ from one airline to another. Sometimes, the rules of the airline may differ from that of the airport you are boarding it from. Here is what happened to me. I had the Smatree portable charger for the Mavic Air, which has a capacity of 158Wh. Airline rules stated I can carry a lithium battery up to a capacity of 160Wh but need prior approval for anything above 100Wh. Meanwhile the airport's rules state I can only carry a battery with a capacity of no more than 100Wh. What was I to do? I emailed the airline a week before my departure date. I got no answer. I sent a reminder five days later. Still no response. I print out the airlines rules about batteries. I arrive at the airport, and at the check in counter, I raise the issue and whether I needed the airline's approval for carrying the battery onboard . The gentleman at the counter takes one look at the battery rating and tells me I cannot travel with this battery since it is more than the allowed capacity which is 100Wh. I protest, saying the airline rules state otherwise. He says he is sorry but I have it wrong. I pull out the print out of the airline's rules and show him what is written there. He says I will need to talk to his manager. So I go to this manager who, upon hearing the issue, says I got it all wrong and the limit is 100Wh. I take out the printout once more, he reads it; opens the website on his computer to confirm, makes a call to someone, and finally tells me yes, I can carry the battery onboard. I thank him and ask if I need anything from him if I have problems at security screening since the airports rules differ from that of the airline. He says I should ask them to give him a call if I encounter any issues there, writes down his phone number and gives it to me. At security screening, they did not ask any questions about the batteries but confiscated a small motorized screwdriver set (bought for 50 Euros) which I had mistakenly included in my carry on bag. That hurt but I was glad I had all my batteries - I had with me three Mavic Air batteries, the Smatree portable charger, and a Celestrone Power Tank rated at 84Wh.
TL/DR: Always check the rules of the specific airline you will be flying with and prepare accordingly. Also, print out their rules and take it with you; don't assume staff are familiar with the rules. And as long as you comply with the rules, stand your ground if staff tell you otherwise.