It would be my advice to not use a third party outfit to do that work. There should be contact info on the unit itself to lead you to the genuine refurbisher. If you have first hand knowledge of a third party outfit that is legitimate then that's fine but the fact that you have posed the question here then I would say "Better safe than sorry".
This is one of those things that bother the hell out of me. A plb cost about $230 on sale and they want $150 to do a battery swap. I opened the unit, it was standard lithium cells connected by Ni strips. Lucky I know a guy with a battery spot welder. I got the NI strips on Amazon and cells for about $6 at bulbs and batteries. Welded them up and all set.
The EPIRB is likely the same. Standard industrial cells that you can likely buy. You have to weld them though. They want like $200 to do the job. Sorry, but that is a screw job.
A lot of people are nervous as if you do this wrong, you can have a runaway. I asked the guy at batteries and bulbs why they don't do this. They are nervous and likely rightfully so as it would be difficult to control at so many locations. Still, this is a good business for them. I'd build a specialized box to do the unit in. Good business opportunity if you ask me.
I used http://www.statesidecm.com/
I agree the price is crazy, but when I bought EPIRB, it came with a $150 rebate coupon to use when the battery needed to be changed. Their regular price is $299 plus shipping.
It was a quick turn around. Next time I’ll just buy a new one, and add the old one to the land fill.