I now have rechargeable Resound HAs frrom Costco, but my previous ones were Rexton, which used replaceable batteries. (I still keep the Rextons in case the Resound need to be serviced for any reason.)
The Costco/Kirkland batteries are in an easy-to-open package with a flap on the back that you fold down and then rotate the clear plastic "cylinder" to expose a battery- basically a Colt SAA for HA batteries! Easy-peasy.
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(I'm in Canada so the instructions are in English & French)
Point well taken about the rechargeable batteries not being replaceable, though. The Resound cost me $2k CDN (I think they're about $1700 USD) but I don't want to have to replace them just because of the batteries! Maybe by that time the Right to Repair movement will have got enough traction to require that they be replaceable- preferably by the local vendor as you wouldn't want to be without them for a week or so while they go back to the mfr's regional repair shop.