Reanimating Dead Tissue

I have an older TENS unit and need a battery. Std. battery is a BL-4C 720mah 3.7vdc LI-ion rechargeable. The batt leads are soldered into the unit’s board. It is a very small battery. I cannot find a direct replacement…

Googled for “BL-4C Ebay” and got a cell-phone battery as a first hit. Are you sure you can’t solder leads to the contacts on the side? True, you should be carefull not to heat them up too much. Or

to be totally safe [Mcgyver some thin press-on pin-contacts in the case perhaps? … 0675876950

And I’m no EE either (schooled as ME, IT-guy now). As long as the battery chemistry and battery voltage match a larger capacity will only enhance the endurance of your device.](MacGyver (1985 TV series) - Wikipedia)