There's guidance from the MHRA on this; maybe you've read it. Personally I wouldn't rely on a sales brochure or technical person giving me verbal assurances if I were going to install generic or custom packs into all our defibrillators for example. Not that I have the authority to do so anyhow.
I'd need some evidence that the batteries are not just compatible that they are "equivalent" and "fit for purpose", i.e. they have performance and characteristics that meet or exceed the medical device manufacturers origninal battery specification; as well as being "compatible".
You have to be careful what suppliers mean by "compatible" and obtain the information that proves that the battery is "like for like" in terms of specification. For example a compatible battery may work but its specified lifetime may be shorter than the original battery specification.
In my opinion you can't assume that all suppliers will be sourcing a particular type of generic battery from the same manufacturer. Even if the generic number on the side of the pack appears to be the same. Specifications may vary between similar batteries from different manufacturers.
I would be more inclined to ask Euroenergy why they don't manufacture their own medical-grade equivalent for the NJ1020HP since they appear to be highly reputable, registered with the MHRA as a medical battery manufacturer and guarantee batteries for 2 years. I'd still ask questions though!
