Quick overview from the supplier:
Ajax Wireless Security Range Extender "ReX", Black
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https://ajax.systems/products/rex/#specBlock
Compatibility - All Ajax hubs
Maximum connected devices (in a system with one range extender): Hub, Hub 2 — up to 99; Hub Plus — up to 149; Hub 2 Plus — up to 199
Max number of connected ReX per hub; Hub — 1; Hub Plus/Hub 2/Hub 2 Plus — 5
Power supply: 110-240 V from mains or 12 V when using 12V PSU for Hub/Hub Plus/ReX
Built-in back-up battery: Li-Ion 2 А·h Up to 35 hours of offline operation
Operating temperature range: From −10°С to +40°С
Permissible humidity: Up to 75%