SLA batteries have a self-discharge rate of about 5% per month.

 

Deep discharges are not good but a few are no problem.

 

Storage in a somewhat discharged state results in sulphation.

 

The working lifetime of SLA batteries is typically 300-500 cycles, depending on the depth of cycling and the operating temperature.  That is, the charge capacity slowly falls as the battery is cycled.

 

SLA batteries are resistant to damage from minor overcharge.

 

Conclusions:

 

1. Don't worry, be happy.

 

2. Use a float charger if the battery sits unused for long periods of time - like in the winter months or during hurricane/tornado season.

 

3. Even though the battery voltage test may be good. Consider the cycles count as a good way to estimate when to change batteries.  In my case, my main battery is just over 3.5 years in service and I have landed with it 310 times.  Since I don't do pattern work, landings are a good measure of "cycles".  In many cases, mere age may not be a good measure of battery "lifetime."