Readily accessible in the security office immediately outside the elevator, along with cybernetic upgrade stations. Later in the game it's a good idea to remember this one because you can easily get to it from the main elevator shaft, arguably more than the one on Med/Sci - Medical (Hybrids will respawn in the latter, but not at Hydroponics).
There is a recharger in a very good location, in the central crew lounge with the upgrade stations. This room is only accessible via a gravity lift, so it will always be safe and enemies can't attack you while you're recharging. The drawback is that there is an enemy respawn point immediately outside the doors in front of this gravity lift, so you'll hear them down below you.
Garden: in the security-encrypted room in the southwest corner of the map, located right near a bulkhead that leads back to the main Recreation area and specifically the elevator shaft. This is also a good one to remember. If you're working out of the elevator shaft as your main base, simply take a left and go down the long hallway to this bulkhead, then pop into the security-locked room (you will need to hack it; if you have an ICE pick hack device save it for this room - also accessible by using the maintenance tunnel underneath the observatory). Also use an surgical bed activation key on the surgical bed between the elevator and this charger, and you're good to go.
Athletics: located behind the pools, which you can only access by crawling through a maintenance shaft from the left basketball court.
Mall: in the security office near a turret and a surgical bed. This is a good surgical bed to use an activation key on, as a result.
In the hallway between the elevator and the tram car, you can't miss it. This isn't the best recharger to use because it's a very active respawn point, usually for poisonous Annelid spiders but other times explosive protocol droids (nothing fun to take out). Though it's on your way back and forth to the tram so you might want to charge on the run.