24 volts with one battery losing voltage

[DSLHEAD]

i have no extras hooked up (except existing 12v headlights) but my driver side battery keeps on losing voltage. i put in a new ground: battery to body to engine. rebuilt the alternator (new brushes) and replaced the headlights (12v).
alas, still not enough amps to turn over engine every few days!!
it's now winter up here and i am stumped and not going too far!
tell me there is hope!
dp.

 

[John Galt]

What model vehicle
what brand of battery

 

[mobi-arc]

With the vehicle OFF lift the ground cable off the negative terminal. Place a test light between the lifted ground cable-lug and the ground post on the battery. If there's enough power to illuminate the test lamp, there's something in the electrical system drawing too much power. Also, an internal battery short could be the culprit.

 

[Ron R]

How old are the batteries? Have you taken them to a battery-shop to have a capacity-check?

What happens if you exchange the batteries in position. So drivers-side to passenger and vice versa.
Does the problem stay with the battery (so now your passenger battery is loosing power) or is it still the drivers side.

When the problem moves along with the battery,suspect the battery (internal damage)
If the problem stays at the drivers side, suspect the system.
Then there might be a hidden tap (short - car-radio memory - anti-theft) you are not aware of and further investigation will be needed.

 

[Frode S]

When I had this wery problem, the fault was bad contact in the cable between the batteries. The original cable is CRAP.