Battery Getting Weak Sitting

[Drg racr]

If my daughter's 2000 Ex sits for more than 5 days, the battery gets weak. I changed the battery, cleaned the terminals, checked all the connections, made sure that nothing is left on, ect. It still happens. Anyone know of common shorts than can develop?
2000 Ex, 2WD, 4.0L OHV, auto

 

[Turdle]

How old is the battery? Since the PATS system is always using a bit of power, this is a sure sign of a weak battery. You might have it tested.

 

[radman]

Hi Drg racr,
Start by pulling the fuses that keep some electrical items powered all the time, radio, PATS and so forth. As you pull fuses pull the ground wire of the battery to see if you get an arc, if you do you have still not found the draw. Do not forget to close the doors when doing this as the cabin lighting will give you a false check.

 

[SWIGIN]

My 98 did the same thing And it cranked slow so I bought a battery since it had the wrong size battery in it anyway.

Not fixed

As far as the drain, I couldn't find anything so since it looked original I replaced the alternator next.

Not fixed


My cables looked good but I decided to clamp a jumper cable from the negative terminal directly to the engine and try starting it. It started like it was brand new.

So I made a short ground wire that goes from my negative terminal to the aluminum power steering bracket to ground the motor. A year later it still works great but I need to make time to replace the original cable.

 

[Drg racr]

Now that you mention that, the PO replaced the ground cable and its ground to the starter.

 

[SWIGIN]

Then I'd check all contact points for being clean and tight.

 

[Flash]

Check the fluid levels in the battery too, if it's serviceable.

 

[J_C]

A common problem is alternator failing, which can keep it from charging efficiently and/or drain it while off. A bad cable connection can make for hard starts, but would not cause the battery to drain excessively.

First it would be good to gather some data with a multimeter. Measure battery voltage with engine running for a while, battery voltage when engine shut off, voltage after it sits for a few hours, trying to determine if it's not charging right or is but discharging at a high rate.

You can also disconnect the alternator then complete the circuit with multimeter in current measurement mode, engine off, to see if it's draining. Same goes for the entire vehicle, multimeter in series to measure current then as you pull fuses and relays you can see if the current rate changes to see if any particular circuits have excessive current drain.

You can also or instead, measure right at the fuse or relay contacts but it's less fiddly to just do it at the battery if you have a helper to tell you what the current is doing as you pull fuses so you aren't running back and forth to see the reading. It should be under 200mA total at least, more likely under 100mA with everything off.