Dji does not have an OEM batter for S900 and there are many issues with batteries in terms of size, performance, weight and price.
So;
What battery do you use on S900? Please briefly explain why.

TBM 6s 15,000mah packs. These packs come ready with the xt150 & as150 already installed. Got about 12.5 minutes and put 70% back. The pack weighs 1920g and the dimensions are 7" x 3" x 2 1/2" . Fits perfect on the s900 and cant beat the price. This is a fully loaded s900 with GH4 HD gimbal.

If you want close to 20mins they have a 21000 that is just a little heavier....

TBM 6S 15C 15000 mAh. with XT-150 Plug seems to be out of stock.
Do you have an alternative choice on batteries?  

If you want crazy flight times look at their 21000...

Get whatever the biggest is

Hi, if you fly intensively ( commercial work) on S900 you might consider 12 000 to 16 000 mAh to keep the machine light and powerful without dressing the mechanics ( arms supports, dampers, motor bearings).

If you fly not too often 20 000 + are acceptable, but you will need in that case to make sure that your S900 is perfectly centered ( balanced) or you will encounter very quickly troubles on motors bearings ( M4, M5) and their ESC's that will get very hot.

20 000 's + are more likely to be used on the S1000 but on the S900 it's a little heavy and there is a lot of early maintenance to do on these configurations most of the time ( just my 2 cents)

TBM packs are very good and so are Tattu ( Gensace / Grepow) batteries. The 12 000's are really a nice fitting to the S900 on my opinion with a good balance between weight / flight time / machine components " duration".

Best regards,
fabien

Those are great reviews guys.
I am thinking of using 2 packs of Turnigy nano-tech 8000mAh 6S 25~50C
any suggestions on that?

Hello Jenk,

that might work for you but you will have to make a new power plug to connect the battery's together. As well as the weight might be
higher then a single battery...

Too many choices as well as the price might be higher for two then one battery.

just my two sense

I got my self on Ebay two 6s 10ah battery's. One cell seem to be pretty low on the healthy part.. But works.. Cause im not using any heavy on the s900 right now and as s900 it self it aint no racing plane/craft. So the C as 25-50.. Works sure... But the higher than hmm around 25-30C you dont really need so much.. At max if i remember right the craft uses 3000w. So the C on discharge just say's how high the battery can give out.. How ever, do know that this value aint always right.. ;)