Hi Andrea,
If you check out the [guide|111761|Battery Replacement|new_window=true] guide on the device page, it calls out the battery used.
[quote]Two new batteries. AAA size Ni-Mh with tabs. Originals were suppo 700mAh, I replaced with 900mAh.[/quote]
That same guide includes a link for replacement batteries that match the description, only they're a bit higher capacity, 1000 mAh rather than the 900 in the guide.
[link|https://www.amazon.com/Exell-Rechargeable-Batteries-toothbrushes-applications/dp/B010TYV7GW/|Amazon.com: Kastar 2-Pack 1.2V Ni-MH AAA 1000mAh Rechargeable Battery w/Tabs Compatible with Electric Razors Toothbrushe High Power Static Applications (Telecoms UPS and Smart Grid) Electric Moped Waterpik : Health & Household|new_window=true]
If yours are indeed rated at 1230 mAh, these would work but would have slightly less capacity than the old ones. You shouldn't have too much trouble locating exact replacement if you want to match what you have, though.
Good luck; let us know how it goes!