Every organization is going to be different. Some have to use a specific chip because of their software contract. If you use Pet Point for example you are required to use 24 Hour Pet Watch microchips. Other software companies might give you discounts on their software if you use a specific chip. I personally use Found Animals microchips with my small rescue. They are a nonprofit organization, their chips are super affordable ($4.95) and there is free lifetime registration and updates. Some chip companies allow you to register for free, but if you change your phone or address they will charge you a fee to update. This is often a barrier to people which is why Found Animals doesn't charge.
If you aren't already using software you may want to look into Shelter Luv which is super affordable and easy to use. If you aren't ready for software, a basic excel spreadsheet can work to track the chips.
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