Was a starter batt with severe case swelling. The electrolyte was dumped and new electrolyte added. Voltage under charge initially looked good but then took a nose dive to 0.5V after charging over night. Note the damage is increasingly severe as you travel from right to left (neg to pos). Pictures don't show it but case was initially bulged about 1 inch on the positive side about 1/2 inch on the negative side. Charging and pulsing may have gotten rid of some of the obstruction. Suspect battery took it's nose dive to .5V when plates started to clear and sprung back.
Stickers were initially above and below the handle area. You can see the outline of where the sticker covered the flush caps. The caps were removed by tapping a pick tool at the cap/case junction until it punctured through and then prying the cap up. You have to be careful that you don't allow the pick to travel too far lest you damage the plates.
This particular battery is well over 10 years old. After removing the caps it was found to be virtually empty of electrolyte. The tops of the plates appeared to be damp. It initially measured 3.79V. It took one cup of distilled water just to cover the plates in each cell. That is one cup per cell. Immediately after rehydration the voltage jumped to 6.72V. It is responding beautifully to rehydration and pulsing. After 1 hour of charging and subjected to the standardized plier short test, it will drop to 11.10V and rebound in seconds to 12.26. Looks like it needs a bit of pulsing. I'll pulse and charge for a few days and then run the charging voltage up to 15V to stir the electrolyte a bit.
This is a truly sealed flooded lead acid battery. After the stickers were removed there were no flush caps. The top was vertically cut with a 9 inch reciprocating power saw. I used a screwdriver to pop the sections off. Access to the cells are via a square hole. This battery was/is a strong performer used to start my WWII generator and was brought in for the winter to be kept on float and pulse conditioned. In order to reuse it, I will have to somehow put the removed sections back in place after they have been hole cut and tapped for plastic plumbing plugs to gain access to the cells. I may just pitch the old sections and use Plexiglas though.
One cell of an L16 is shown next to a starter batter and the empty case. That negative post looks low because installed in the case it is supported by 1 inch fins rising from the bottom inside the case. The negative plates surround the positive plates in each cell.
Shows a close up of damage to the plate through my rough handling. Portions of the negative plate fell off exposing the grid. That welded wire grid is what can cause high resistance in a batt when it corrodes. In both pictures you can see evidence of stratification. This cell has been laying in the horizontal for weeks. The dampness at the bottom is the slow to evaporate acid. You will note the top half is bone dry where it had been exposed to extremely low SG electrolyte.