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, About This Mac, More Info..., Hardware, Power should produce a display like this, telling how many cycles are on the battery, and condition. Regardless of cycle count (300 is considered 'average') if the battery won't hold a charge, the message will probably read 'Replace Battery'
If no battery info is displayed, it's absolutely time to replace the battery.
The display shows a 2-year old replacement battery which has lost over 20% of original capacity.
A new battery should have about 5500 mAh capacity.
I've only upgraded mechanical drives, no SSD's yet, so I can't help you with that question. I've purchased several RAM and disk upgrades from OtherWorldComputing (www.macsales.com), a great source of info about upgrading Apple hardware.