"BTW these sort of problems were common on Brittish sports cars in the 60's, ask me how I know."
Same here!Along with VW Beetles and Rabbits
But I had every other problem too,including having to tie on a generator on a TR 4 to get home,limping to the shop in 4th gear because the input gear was stripped,coasting to the ramp with a stripped pinion gear,a stripped wire wheel adapter,etc,etc,etc.!I [promise I didn't drive it that hard,must have been the previous owners!
But a fun car anyway!
Okay,this sounds more like a problem with over/under charging,if it is being driven daily:
" It is chronic, but very slow. I can replace the battery and it takes approx 3 weeks before the battery will have drained enough that it won't turn the engine over. Once it is drained, it has to be jumped or put on a battery charger but only takes a few hours to kill it again. "
Sounds like it is over charging and boiling the acid out.
That will ruin a battery FAST!
Do you get a sulfer smell from under the hood?Is the battery box rusty?Is the top or sides of the battery wet or bulged? All these are signs of over charging.
Be very careful around the battery because one will blow easily under these conditions.
Keep a water hose where you can find it,or someone to wash your face off fast if it goes up on you.
Wear saftey goggles!
I've never had one blow on me,but I have seen lots of them,and my father has had it happen a couple of times in the 60 years he has been involved with automotive repair and parts sales.
(I had a Rabbit that started to over charge,and ruined a battery before I could get back to Locust Grove from Macon. The main clue was the sulfer smell that I thought was an odd smell for that part of the state!It was a battery being "hard boiled").
Put a good battery in it,and use a volt meter to see what it is charging with the engine running.
Older cars should charge 13.5 volts (- or +).
A lot of new cars are running higher,14 or a little more. If it is charging 15 with no lights etc on,it is probably over charging it.
If you will let me know what body style it is (My 2001 service manula doesn't show a Town and Country) amd which engine it has,I'll try to find out what the charging voltage is supposed to be,so you can check it.
The newer cars have the altenator controled by the on board processor (comupter),so it could be a computer problem,ground problem at the altenator,a ground problen else where,or something some one did while installing any radio,remote start,working under the hood,etc.
Like ar-wrench said,this type problem can be hard to nail down,unless there is an ongoing problem that the delaers know about.otherwise,it is all look until you find it work,even if you have years of experience ,but as fast as cars are changing these days,even that isn't much help sometimes!
Robert.