I am not someone knowledgeable, and I would not trust my opinion. However, since noone else has posted here, I will share my untrustable opinion with you.
If I were in your position here's what I would do.
1. I would check the voltage (with an multimeter) ideally against another battery in a similar state. Assuming it is providing a reasonable voltage (between 11.5-14) that will show that it is able to provide an electrical charge.
2. I would clean the surface this battery and charge it with a tricklecharger. I would possibly pour a light coating of baking soda around the battery terminal beforehand. I would charge the battery "fully" with a trickle charger and monitor the status of the battery as it charges (to see if it leaks any acid). Assuming it does not, I would "equalize" (I could be wrong about this) by unplugging the charger and recharging it. I would do this a few times. If no battery acid spills then I would presume it is okay and I would make sure this is in a somewhat ventilated area (aka not where I will be breathing air).
Once again, don't trust my opinion but perhaps it will give you an idea.
Also here's a picture of a battery.
My guess would be that if it produces consistent voltage it will probably just have a crooked block thing inside, which would make me assume that the upper section is corroded, which would make me assume that it will go bad sooner than later.
In case I didn't make it clear enough, I have very little education in electronics and should not be trusted without a big grain of salt.