Why does my car battery keep going nearly flat.even after I buy new 1 week latr it drains or alternater cant keep volts up

There is possible solutions: the battery is old and nearing the end of its life. or a parasitic drain. The drains are difficult to find. go to you tube and watch videos on battery drain when car is off. This will require some time but doable.
Car batteries will give indications of going bad then they are dead, you cannot recharge them ( regardless of what some people say)

Good luck

Usual culprit is boot (Trunk) light.If not, try disconnecting battery and if a spark jumps as you take the lead off it shows there is a power drain. If no power drain it points to a faulty battery.

MAYBE THERES AN ALARM SYSTEM DRAINING BATTERY
BEST WAY TO CHECK IS REMOVE BATTERY LEAD ,AND WTH EVERYTHING TURNED OFF SHOULD BE NO SPARK WHEN YOU RECONNECT

If you have a drain on your battery , it would not take 18 months for the battery to go dead . What do you mean The battery gauge in the dash shows only about 1/2 power, When ? When the vehicle is running ? Not charging ! The battery gauge as you call it has nothing to do with the Battery . That's showing how much the charging system is putting .The volt's indicator is controlled by the PCM - engine computer . With the engine running should show 14.1 volts .if your only seeing 7 the charging system isn't working. The alternator is controlled by the PCM as well ! Have it check by a GM dealer .

Hi.

Make sure that you also replaced the battery. Battery elements may be shorted inside. That will result in battery draining even if the alternator is working.

If you have already replaced the battery check power across battery terminals with engine on and revving above idle.You should read voltage in a range of 13.5/14.4 volts when engine is revving at about 2K rpm.

If the voltage is still wrong after replacing alternator and battery check the voltage regulator connected to the alternator. Here the part.

If battery, alternator and power regulator are OK, test wiring to find out if there is a short to ground that is draining the battery while you drive. This fault is quite unusual with your symptoms. Check battery, alternator and voltage regulator first.

Regards.

Ginko

had the same type problem with van that had security system on it.. even if not armed it would drain battery if not driven at least once a week. this might be same type of problem.

Likely a crushed wire or switch within the damaged door is draining the battery. The easiest fix would be to find a replacement door at a wrecking yard--you might even be able to get one in the same color.

Well, if the alternator belt squeaks a little, it cannot be actually charging properly, resolve that...

First steps would be to fully charge the battery and measure the voltage. Turn of vehicle Disconnect the negative terminal overnight, for a night or two.

If battery still dead, focus on the battery.
If battery is not dead, put a volt meter between the negative terminal and cable and measure voltage... do not be mislead by interior lights, or clock, pull those fuses, during testing...

Anyways, keep going until you find a drain.

The alternator has diodes that can cause a drain...disconnect for testing purposes...

NEVER run the vehicle with the battery cable dicsonnected.

Doc

the camera takes 1.5v to operate it
anything less the camera will shut down
recharge batteries are only 1.4v so at full
recharge it won't last long
The best batteries are litheum that have the right
volts and capacity to keep the camera going.
try turning or the camera stablizer setting...
might save your battery power.

difficult to accurately *****, you need to get the charging checked, even though you have a new alternater the problem could be as simple as the charging light not working, which causes the alternater to initiate. or you may have an electrical component staying on draining the battery.