When I watched my old man rebuild them he always replaced all the
plates. Seemed pretty straight forward, unbolt the box cap then the
retaining bolts for the plates and pull them out.
Dump the electrolite, flush case with a neutralizer, put in new plates
and acid and bolt it all back together.(Of course these units were
designed for ease of service)
I did years back restore an old German motorcycle, prewar, called a
Fluka and it had a glass case battery which we had to have custom
plates made for.
"Boltable" plates would be useless where very high current demands
were present, as in telephone exchanges. While each individual battery
was designed to connect to the adjacent cells in a series battery
using bolts, this practice was shown to cause major problems due to
the bolted joint developing high resistance. Consequently, both the
individual plates in each cell were lead-burned together as well as
the connections between cells in order to minimise any added
resistance. The end connections to the copper distribution bus-bars
were the only place bolts were found and these were constantly checked
for temperature rise or signs of oxidation.
I was once working in an exchange in the late 1950's where bolted
battery joints were still in existence and accidentally dropped a 12"
crescent spanner right across the bus-bars feeding several suites of
equipment. There was a mighty loud bang as the spanner was melted and
every switch dropped out in the affected suites. In the time taken for
the 500A feeder fuse to blow every bolted joint in the 48V duty
battery had molten lead blown out of it due to the heat generated in
the minute resistance in each joint. The battery room was filled with
smoke and I was not very popular with the maintenance staff. Needless
to say, after that episode, the battery interconnection joints were
lead-burned.
If we take an extreme case where each bolted joint has only 1
milli-ohm resistance (this is a "very high" resistance in this
environment) then a 48V battery of 24 x 2V cells would have roughly 48
milliohms total resistance in the bolted joints. In heavy traffic a
current draw of 500A would drop 24V across the joints alone which
would stop the exchange from working. Any resistance at all in the
battery would also lead to cross-talk between circuits since the
battery is common to all circuits.
Typically, the internal resistance of a 48V exchange battery including
all joints between cells would have a design volt drop of 100mV at
maximum current drain. For a design goal of 1000A maximum drain this
would equate to a total internal resistance in the battery and all
connections of 0.1 milli-ohms, and that is hard to achieve in
practice.