Is 5034LC the same as CR1216?

Yes. 5034LC is another code for the same cell: lithium (Li-MnO2), 3 V, 12.5 × 1.6 mm.

Is DL1216 the same as CR1216?

Yes. DL1216 is another code for the same cell: lithium (Li-MnO2), 3 V, 12.5 × 1.6 mm.

Same 12.5 mm diameter, but 2 mm tall instead of 1.6 mm. Only if the holder fits; thinner cells can lose contact.

Same 12.5 mm diameter, but 2.5 mm tall instead of 1.6 mm. Only if the holder fits; thinner cells can lose contact.

No. Rechargeable Li-ion: 3.6-4.2 V and far less capacity; only for devices built for it.

CR1216 is a 3 V lithium cell with a typical capacity of 25 mAh.

12.5 mm across and 1.6 mm thick.

CR1216 is the same cell as 5034LC, DL1216 and ECR1216, so any of those codes will fit; no other cell here is 12.5 × 1.6 mm at 3 V.

CR1216 at actual relative size: 12.5 mm across, 1.6 mm thick. The dashed circle is a US quarter, 24.26 mm across (US Mint coin specifications).

The same cell under another code. Any of these fits, whatever the brand.

Same diameter, different thickness. These are not drop-in replacements.

Cell	Size	Verdict
CR1220	12.5 × 2 mm	Same 12.5 mm diameter, but 2 mm tall instead of 1.6 mm. Only if the holder fits; thinner cells can lose contact.
CR1225	12.5 × 2.5 mm	Same 12.5 mm diameter, but 2.5 mm tall instead of 1.6 mm. Only if the holder fits; thinner cells can lose contact.

These are the same size or a similar code, and they are not equivalents.

LIR1216
Rechargeable Li-ion: 3.6-4.2 V and far less capacity; only for devices built for it.

Used in some lighted watches and some LED decorator lights (electronic tea candles).

Is 5034LC the same as CR1216?: Yes. 5034LC is another code for the same cell: lithium (Li-MnO2), 3 V, 12.5 × 1.6 mm.
Is DL1216 the same as CR1216?: Yes. DL1216 is another code for the same cell: lithium (Li-MnO2), 3 V, 12.5 × 1.6 mm.
Will CR1220 work in place of CR1216?: Same 12.5 mm diameter, but 2 mm tall instead of 1.6 mm. Only if the holder fits; thinner cells can lose contact.
Will CR1225 work in place of CR1216?: Same 12.5 mm diameter, but 2.5 mm tall instead of 1.6 mm. Only if the holder fits; thinner cells can lose contact.
Can I use LIR1216 instead of CR1216?: No. Rechargeable Li-ion: 3.6-4.2 V and far less capacity; only for devices built for it.
What voltage is CR1216?: CR1216 is a 3 V lithium cell with a typical capacity of 25 mAh.
What size is CR1216?: 12.5 mm across and 1.6 mm thick.