I think George you are doing the right thing during winter, to keep your battery charged up!
If you are concerned at all about the Alternator'* charging ability, an easy test is to start the car and put a serious load on, by having all the lights on high, heater fan on high, rear defroster on, and radio on, and then check the voltage that is coming out at idle and at 2000 rpm
. What are your car readings now with load on?
If you have removable caps for water, take a peek in there (Use safety goggles please) to make sure your water level is slightly above the cell line. If additional water is needed, add distilled water.
If you really want to know the specific gravity reading or state of charge of a battery, an inexpensive hydrometer will tell you how your battery is doing on each cell
In the photo below with a battery that has been trickle charged over night, it is well above the good mark or 1.300 reading!
Many do not realize that a 10 or 15 minute run to the store is really not charging up your battery very well at all. Especially if the car is occasional use or will sit for a few days!
Most cars with security systems etc also have some minimal drain placed on the battery overnight too. Once the car has been off for 10 minutes, look to see if the battery voltage is holding or dropping, indicating a possible major drain down. (electrical drain or bad cell)
So charging up occasionally is a good thing! Always look for an intelligent charger or one that goes green when full.
As Richard stated many lesser expensive batteries may only last a few years and I agree that higher CCA
(cold cranking amp) battery (that can fit) is the way to go!
That being said using a trickle charger on your batteries will extend their life, with proper maintenance. Including keeping your terminals free from corrosion!
Mike Mentioned Extreme Cold
and here is the straight goods that explains the relationship between CCA and required power to start on cold mornings!
I also have a battery load tester and after charging overnight I can apply a 100 amp load and take a reading.
There is no fooling this tool. When your battery is weak it will tell you by the scales how many CCA are available from that battery!
If you want to spend more money for a much longer lasting battery, all the new series of AGM (Absorb glass matt) will offer much better performance, and are maintenance free. AGM'* wont vent like conventional lead acid batteries, so u will not get corrosion on your terminals either. I use a top of the line Odyssey in The Pk Ave, but Enersys makes the same for much less dollars in the US as a Sears Die Hard Platinum (AGM)
In the photo below I am charging with a C-Tek that is ready for AGM batteries as well. These chargers offer a desulfation wave to restore weak batteries too!
Possibly too much information...But that is just me..don't get me "started" by battery topics LOL..
I hope this may be helpful!!