Ensoniq batteries

i have a few questions.
do the batteries have a shelf life?
when you say the battery is new, how new are we talking?
if battery is a panasonic ####, can it be replaced with duracell equivalant?

i need to replace my ensoniq TS-10 battery.

Batteries have a shelf life as they self-discharge with time. Lithium coin cells typically have a very long lifetime, though, so probably nothing to worry about.

The brand of batteries does not matter to your synth. Only the (standardized) form factor matters.

If you haven’t done so yet, I would recommend you to open the synth before ordering a battery and check if a battery holder is installed. The battery for the TS-10 sold by Syntaur is a coin cell that needs to be soldered to the board, like the original batteries installed by Ensoniq. However it is quite common that these synths are retrofitted with standard CR2032 battery holders where the battery can simply be popped out and a new, standard CR2032 that you can get from a local store be popped in in a matter of seconds. For example two Ensoniq SQ-Rs that I looked into both had a battery holder instead of the original soldered battery, so it seems like this might be a common modification.