It is time. Now......
If you lived in Aridzona, you would have already replaced the battery.
The rationale is that acid does things for a living. Like eat lead battery plates for one.
An ideally maintained flooded lead acid battery living in a 0C 32F environment will last around 30% longer in a storage environment, than a battery in an average of 25C environment. Ideally maintained means maintenance charging, top charging, and stirred once in awhile.
Ice cold battery electrolyte will not affect much until it warms up (body heat). 50C (122F) 1.275 electrolyte is DANGEROUS. Like several hundreds of times more reactive.
5-years is at the end of the down-slope ramp of reliability. Definition: You will get more service time out of the battery. Just don't put yourself in a position where a failure could cause hardship or hazard, if you decide to press for 100% of service life.
