Lead acid batteries will have a rotten smell after shorting out - more so in wet ones, but SLA will smell the same. If you wait to the point that an SLA smells

Lead acid batteries will have a rotten smell after shorting out - more so in wet ones, but SLA will smell the same. If you wait to the point that an SLA smells, it has probably expanded and caused internal damage to your UPS/server rack, albeit minor if you can manage to get it out without dismantling anything.