Accidental Science Fair Project

Our Roomba is having a battery problem: It runs for about 5 minutes and then is out of juice. When it was new it would go for a long time--like you would get bored with rescuing it from carpet tassels and shoelaces before it ran out of power.

I figured that the best course would be to do a deep discharge on the power pack and then recharge it to see if it works better.

I was at a loss at first about how to discharge it: The machine will not run at all when the power is low, and I didn't want to just short out the leads...What I finally did was connect jumpers from the battery to probes in a glass of salt water. I could tell it was working because I was seeing bubbles forming around the electrodes under water.

This got me thinking. What if one were to do this in a closed environment, so that pressure could build-up? At some point, I would expect the pressure to cause the electrolysis to stop. This would be easy to measure with a pressure gauge. What would be (if any) the relationship between voltage and pressure?

Safety: Yes, I realize that a high pressure mixture of oxygen and hydrogen with electricity in the mix, could be an explosive combination. This would suggest that the total size of the apparatus be kept small. An added benefit would be that equilibrium would be reached sooner as well.