It has been a few years since I have been in those sub-stations, but as far as I know they are still using the same design.
One interesting history about these batteries is that while these huge batteries have an amazing long life expectancy (something like 20 years) there is a limit to how long they last. In general the rule of thumb is supposed to be that when one cell goes bad replace it and take note of it, but when a second cell goes bad replace the entire pack.
The interesting history is that in one of the sub-stations in the North Hills of Pittsburgh many years ago the pack was requiring distilled water to be added to several of the cells at a rate that was alarming, and some cells had been replaced. The person in charge of the crew that among many other jobs also maintained these batteries, had put in a request to have these batteries replaced, but the people who controlled how the money was spent did not OK the spending. So he put in another request along with stronger language about how important these batteries were, and it still was not approved. This request and rejection went on each month. Then one day there was a storm and of course as often happens during a storm a fault on one of the main lines caused a huge surge in power being drawn. The breaker (thing something about the size of a refrigerator) tripped, and as usual after the breaker is tripped sectionalizers that can not break fault current but can open the circuit once no power is flowing, sectioned off some of the line, then the breaker closed to pick up the line and see if the fault was still on the line. The fault was still on the line. Normally the breaker at the substation would of opened again, and then additional sectionalizers would disconnect more section of the line and the circuit breaker would close to try to bring up the line again. However the battery back failed (one of the cells failed open) and therefore the breaker in the substation would not open again. The fault was still on the line, and with the huge current flowing (think the equivalent power of several diesel locomotives at full throttle) the big electric buss bars in the sub-station began to melt, the huge insulators were over heated inside where the conductors were and began to explode, and the huge transformers began to melt internally.
If someone would of been in the substation yard there life would of been in jeopardy because the insulators exploded like grenades, and the bus bars melted down. When other sub-stations finally dropped the load, six of the seven transformers costing about one-million-dollars each, were damaged beyond repair.
The North hills had to put up with rotating blackout for weeks while these transformers, breakers, buss-bars, and batteries were replaced.
They tried to go after the foreman in charge of the group that maintained those batteries. He provided copies of each months request for batteries to replace the entire battery pack, and the rejections he got back each month. And he was able to keep his job. AND for some reason, from then on he had no problem getting request to replace other battery pack approved, in fact the people who approved such things suggested that he replace those battery packs in all the substations that used them.