Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: What batteries to buy?
Document: We had to buy this extra headphone to make a set of two for us to use while watching television. We acn both now hear what the people are saying on all television shows.
I bought Sennheiser before. The headphone as a whole is great. The ear pads are not so great as the tabs holding them on break off easily but I would buy again.
I bought a separate set of rechargeable AAA batteries to ensure i would never be stuck without a charged headset.
I love these headphones. I bought the extra set for my wife. Since the batteries last for hours, and are simple to change in an emergency, I didn't have to spend $100+ for an un-needed base station/charger.
Very good buy, it definitely complements the main unit and allows 2 people to use the different headphones. One problem is it is sometimes difficult to get both headphones to work at the same time. They are designed to block out any interference and they can end up blocking out each other. That means you have to re-establish contact to the transmitting unit again. It can be a pain to do this again. Overall I would reccommend them and when they work they are excellent.
I own both the 170 and the 180 and they're both great headphones. If I could do it all over again, however, I would buy only buy the 180s. They are wonderfully comfortable with their felt ear pads. The 170s have the fake leather padding which can be uncomfortable after a long period of time. The other great thing about the 180s is that they don't block out all of the sound in the room which is great especially if you're waiting for the pizza guy to ring your bell!
These headphones are perfect for laying in bed to watch tv while are children are sleeping. I like that up to 4 headphones can connect to one base. The sound quality is really good, better than i thought possible. My one complaint is that these headphones did not come with rechargeable batteries. The listing says they do, but mine did not.
It's a minor inconvenience.Each headphone has two AAA rechargeable batteries. I put one set of headphones on the charging station and just take the batteries out of the other and charge them in a generic charger.Great product. The kids are able to sleep at night, and we get some peace because they wear them when they are playing video games or watching cartooons.
These headphones are amazing. They are comfortable, fairly durable (we have three pairs) and easy to operate. We use them a lot, as our 18 month old sleeps off the living room, and is a light sleeper. The charger keeps the batteries fresh without having to remove them, and the one touch on/off buttons are simple to operate.The sound quality is better than my wired HD555's, and the range is excellent.
I didn't want to put a generic pair of rechargeable batteries in expensive headphones that might have issues when using the sennheiser recharge station. I still have not heard back from them, one week should be more than enough time to respond. Great headphones, just hope nothing ever goes wrong with them or I doubt I will get any help from this company.
Answer: AAA **RECHARGEABLE** - any kind will do. I bought a set of Sanyo batteries with a separate charger from Amazon.