If no sign, it'll be fine. The major fear of putting a lead-acid battery on its side is it spilling sulfuric acid onto wherever it might end up. It won't hurt the battery itself, other than if it loses acid. If you are sure no acid has leaked, then it's probably a case of "no harm; no foul" and you got lucky.
Why would lead acid battery leak? If your friend’s battery had expanded and leaked into the battery box through the emergency venting holes provided on the battery it most likely means that the battery had a serious internal fault or the charger was not the appropriate charger or even had a malfunction.
Lead acid batteries, including both sealed and flooded types, are prone to corrosion when electrolytes reach the battery terminals. For sealed batteries, this can occur more easily due to the design. While adding water to a flooded lead acid battery, electrolytes can 'jump out' from it, increasing the likelihood of corrosion.
All lead-acid batteries are at risk of sulfation, which causes their inner battery plates to degrade over time, and become less conductive. Sulfation is the most common reason for a lead acid battery to lose a majority of its charge. Just because your battery is down doesn’t mean it’s out completely!
Alan L. Thank you for your question, Alan. Lead acid battery storage is a serious issue but also probably just as importantly is the care and maintenance of batteries. Why would lead acid battery leak?
The plates that are now at the top of the battery are exposed and are no longer immersed in the acid mixture which will lead to plate damage and ultimately battery malfunction. When a lead acid motorcycle battery is laid on it’s side, the acid mixture inside will also leak from the battery.