Hi guys I'm looking for an accessory to hold the battery secure while flying in case the battery gets swollen and comes out .

Any suggestions ?

well shouldn't swell up and the batteries are latched in place and are inside of a container...if they are swelling up that badly that they break free, a strap isn't going to really help..?  

if you are getting puffy batteries, replace them.  DJI offers 6 month warranty, use if it you can. and do not fly puffy batteries.    i only had issue with 1 battery puffing up on me, mavic air battery and nearly brand new... and DJI replaced it for me, of course after the mindf*ckery that is DJI customer service took me on a journey in circles for a couple days... but eventually got sorted out and replaced.  

You could try some velcro

HereForTheBeer Posted at 9-1 19:53
well shouldn't swell up and the batteries are latched in place and are inside of a container...if they are swelling up that badly that they break free, a strap isn't going to really help..?  

if you are getting puffy batteries, replace them.  DJI offers 6 month warranty, use if it you can. and do not fly puffy batteries.    i only had issue with 1 battery puffing up on me, mavic air battery and nearly brand new... and DJI replaced it for me, of course after the mindf*ckery that is DJI customer service took me on a journey in circles for a couple days... but eventually got sorted out and replaced.

Not quite true.

Quite a few threads here and substantially more on the mavicpilots forum from users that have swelling, unusable mavic batteries after a short period of time and normal use.  Significantly more than with the Mavic 1 or any other drone.

They swell up to the point the latches unclip.  If you're lucky only 1 latch will pop and the app will display a warning.  If you're unlucky, the drone will just power off and drop like a brick.
Its perfectly possible to trigger an unlatching by gently nudging the drone, braking or a wind gust in that condition.

All 3 of my original fly more pack batteries swelled to the point they were unusable after 7 months and 20 cycles each.  DJI support dont want to know as its over the 6 month guarantee.  
There were operated normally, never run down below about 30%, never stored charged, original charger, cool before charging etc etc.  Normal use.  Many others are saying the same.

Back to the original post, a few of us have tried straps or tape but they dont work.   The mavic case is flexible enough that it stretches - you simple cant prevent the outwards and upwards stretch which causes an unlatch.  The issue is the contacts between the battery and drone are not very long.  It doesnt take upward movement to disconnect the electrical path and therefore turn the drone off (i could do mine by holding it and gently shaking it).  So although a strap may hold the battery in, it wont solve the problem.

I worked out i was paying $7.50 a flight with my original batteries which is ridiculous.

Hello and good day Ovi 1. Thank you for reaching out and for the inquiry. I hope that you will get the best recommendation from our valued DJI co pilots who uses this accessory for there DJI Mavic 2 drones. Just a friendly reminder that please do not fly your drone with swollen batteries this might lead to an accident during the flight. Have a safe and a happy flying always.