Your old 2600mah cells have declined, so a 2500mah should be okay. That is approximately the capacity of AA rechargables available today.
Do you intend to clip away the bad cell and solder in the new one? If so then the new one really ought to have tabs for soldering. It is hazardous to heat a battery for a long enough time that high temperature can reach its internals. The battery might break a seal, or worse.
Nevertheless I have connected batteries by soldering wires to the terminals. I tin all surfaces beforehand. I use a high wattage soldering gun. I do not hold the hot tip against the surface. I let the tip heat for a few seconds, then touch it to the parts, for the shortest time that melts the solder.