I have just replaced the battery in my Fast Find. I think it is worth it and good enough.
Having an AIS would be useful but I am not going to pay more for an AIS capable PLB. It is a personal choice if you think AIS will increase your chances of recovery.
I upgraded my LJ and safety tether to Spinlock and will upgrade my jackstays next. Spending limited money on prevention is a better policy in my view.
EPIRB is mandatory here in west oz for any trip beyond 400m of coast. The authorities have now mandated that all eligible EPIRB must have GPS enhancement.
Your old EPIRB will not have GPS and so pinpointing location will be far less precise. Now things are different in UK but I think a new EPIRB with GPS and new battery might be a good idea. ol'will
I replaced the battery in my PLB. myself. It's not rocket science and I trust my own work as much as any technician. It was around £10. I'll probably do it again this year.
EPIRBs have evolved a lot over the years and I wouldn't want one without:
1. Multi-constellation GNSS (not just GPS)
2. Long life battery
3. More compact form factor of later models
Most recent ones have:
1. Return Link Service
2. Mobile connectivity
3. AIS local homing
And on the horizon a number of other improvements, some of them significant.
My EPIRB is an Ocean Safety EPIRB1 which is now 7 years old and has 3 more years of battery life. It has the first three qualities but not the last three.
Will I replace the battery when the 10 years are up?
Probably not. This device is a life or death thing. I sail in some remote areas far from rescue services. I think I would want it to be less than 10 years old at all times and as up to date as possible.
If you're never out of VHF range from some coast guard or another, that's a very different use case where a different approach might be appropriate.