Dead shorting a 12v 12ah sla usually gives no more than 25 amps. Those are the same sla's used in APC backups under 500 watts. Dead shorting a big pack of new nicads on the other hand might give a bigger current rush.
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Shorting a lead acid battery should deliver at least 20 times the amp hour rating, for example, a new 7 amp hour battery will deliver at _least_ 200 amps.. and yes, i've measured this.
it sounds like the current delivered is dependant on the resistance of your amp meter..
let us know how quickly a standard 3/32" dia screw driver melts in when you short out a 24 amp hour, 12 volt battery, if it doesn't, the battery is either not fully charged, or its old.
you can download data sheets from respectable manufactures that list this, in most cases its between 30 and 40 times the amp hour rating, anything less means your battery is on its way out. Using walmart as an example , a new 50$ car battery can deliver 500-600 amps at 9 volts... its much less than 30 amp hour battery.
This isn't a case of what type of battery is it, but the simple fact that all lead acid batteries are more or less the same.
Nicd's and nimh cells have much lower internal resistances, and there are D cell batteries out there that can deliver 100 amps at 1 volt, for a nominal 1.2 volt cell.