If the battery is 60% or less that what it's rated for, given its age I would replace it.
A weak battery can put excess stress on your vehicles charging system
That is not true.A worn battery has reduced capacity ,which results in less amperage flowing from the alternator to the battery.The battery reaches the desired voltage sooner (because it cannot store as much energy as it would when new).It's like a smaller battery got installed instead of the original.
Problems do arise with weak batteries (my car gets into limp mode and you cannot control the throttle pedal at all despite the fact that the starter can engage quite normally) but charging system stress is not one of them.
Unfortunately,it is not an easy task to determine how much life a battery has in order to get the full potential from it.
My batteries last 7 or more years with occasional charges or long trips (plus a solar maintainer on the car).Never got stranded anywere from a dead battery yet,but sometimes cell shortage occurs and that's it.Now you start your car normally, half an hour later you have no battery power at all.I guess if someone is afraid of this matter to happen,he could get a portable lithium-ion battery to jump start his car if needed.They are reasonably cheap very lightweight and pretty small in size.