Heat does most of the damage. Months of high under-bonnet temperatures, short hops along Jumeirah Beach Road and long spells parked outside wear a Subaru battery down faster than it would in a cooler climate, and the weakness tends to show up in summer.
Subaru models take conventional batteries that are simple to replace. On e-Boxer hybrids it is the 12V battery that wears out, not the hybrid battery.
We regularly replace batteries in the Forester, Outback, XV, and Crosstrek. Whichever Subaru you drive, the technician tests the old battery first, confirms the correct size and type for your car, then fits and checks the new one while you watch.