I have had my Dymo PnP USB label maker for about 8 years and noticed that I could no longer print as the battery had died. I found a replacement battery but it is £31. As the battery contacts looked the same distance as a PP3, I looked for a Lithium-Ion PP3 with the same 650Mah.
I could not buy a single battery otherwise this would have been cheaper to fix, but I found a 4 pack of 650Mah 7.4-9V batteries on Amazon UK for £14.40 (there was a 10% voucher at the time of purchase).
I placed the PP3 battery in the compartment with the correct polarity and packed the compartment with a kitchen towel to stop the battery from moving, then replaced the battery cover to check it was tight enough.
This seemed to work and the battery charged and I was able to print a label.