I have two large lead acid batteries that crank a standby Generator...They are in series for 24 volts and crank the gen nicely....I charge both with the same battery tender(12v) one at a time.......1.5 amps on each battery..One charges quickly with no problems ....the other spits water high enought to leave the cell hole...
\Both are charged every month one takes 1 hour to charge and the water spitter takes 2 hours...
Also after cleaning both batteries with clean water....A week later a wet film seeps out around the cell holes on the spitter...I try to keep it clean to avoid a path for discharge between cells and posts...Ive tried floating the battery with the battery tender and the seepage is worst...There are no marking on the batterys and I have tended them for 3 years....Lots of tending....Starts the units every 6 months..These are 1 foot by 2 foot each..Comments please
...Charlie

 

One of the batteries is bad.

It seems really simple from here. Two equal batteries, one works well, the other doesn't. One of them is bad, as in "dead cell".

 

They don't spit H2O (water) they spit H2SO4 which is sulphuric acid.

 

If you want to check both batteries , just check the voltage across each battery while cranking. Both voltages should ideally be the same. If not, then the internal resistance of one battery is greater than the other. This will give you a fair indication of the condition of both batteries.
You could also try checking the Specific Gravity of all the cells to help you locate a faulty cell.
When charging - the lead sulphate is reduced back to metallic lead and sulphuric acid on the negative plates & lead dioxide and sulphuric acid on the positive plates. The rate that this happens at depends on the EFFECTIVE surface area of each cell.Any excess current goes to disassociating the water in the electrolyte into Hydrogen & Oxygen (Explosive!!!) and heat. This is what is causing your spitting.

When the effective area of a cell drops below a certain threshold and/or has internal short circuits caused by buckling of the cells or shedding of active material, then that cell is known as a "dead cell" and will gas profusely under load and when charged.

 

Thanks to all replies...All the cells spit..I will try the voltage test under load...
I am going to get ahold of the manufacturer to find the CCA's required...I may have to parallel two auto batteries to do this.. As with the whole world,bucks are tight...And the lead prices are up..My car battery cost $90 5 years ago and lasted 5 years....Replaced it from the same shop $134.....I use to love T bone steak..Now once a year for birthday..Switched from cognac to brandy.....Charlie...

 

Really think you should run a voltage test. For my projects before, I only use Motorola batteries. Those got me finishing my project without much hassle, so I never got to encounter such problems. Good luck!