Hard to start, dead batteries, voltage drop - what's going on?

Hoping for some help diagnosing the following behavior with a '99 4Runner.

A couple months ago it was hard to start and the battery wasn’t fully charging. It cranked but not very strongly and took a few times to turn over. The battery was old so I figured it was bad and replaced it.

Everything was fine for a couple weeks then it started doing nothing every other time I’d turn the key to start. All the dash lights and everything would come on but when I turned the key to start, it wouldn’t even click, nothing. When it would crank, it started up fine. After a while it started taking 5-6 attempts to engage the starter and eventually like 20-30 and then wouldn’t start at all.

I check the battery with a MM and it was reading 3.5v! I pulled the leads off and the voltage started to rise, after about an hour it was up to 8v. But when I put the cables on it immediately drops back to 3.5v. I pulled the fuses one by one, reconnecting the batt cables in between to see if I could isolate the circuit that was causing the drop but no luck. There were a few fuses that were bolted in that I couldn’t get out though.

Anyway, any insight would be great, there must be something that ties all this behavior together, maybe a bad relay or something?


Dirty or corroded cables!!!

Battery connections are the first place to begin when you have a “No Crank” situation. Even
if you have a new battery, if the connections are loose, dirty or corroded, you will not be
allowing the full flow of current to pass thru the connections. The connection may be
enough to turn on the lights, but not enough for the huge flow that is needed to operate the
starter. This is where many people say that they know the battery is good….”because the
lights come on”. This is no more a battery test than licking a 9volt battery. It only tells you that there is electricity…not how many volts or the amperage that flows from the battery.
Jump starting may have wiggled the terminal just enough to allow the current to pass and start the engine, but tomorrow you have the same problem.

First remove the cables from the battery and use a wire brush to remove any corrosion and dirt from the battery posts and the cable terminals. There is a tool with a round wire brush for this purpose, found at any auto parts store for less than $10 http://shop.advanceautoparts.com/p/kd-tools-terminal-battery-brush-kdt201/25980576-P?searchTerm=terminal+brush.
Before connecting the cables, apply a coating of di-electric grease to the battery posts this will keep oxygen away from the connection so that it will not corrode as fast.

It is just as important that the other end of the cables also have a clean connection. Remove the positive cable from the battery again so that you do not short anything out. Follow both cables to their far ends, remove this connection and wire brush the connection and the cable terminal clean and retighten these connections.

If there was work done recently, there may have been an “engine to body” ground that was not installed following the work. These grounds normally run from the rear of the engine to the firewall and are uninsulated and most are a braided wire. If any of these are found unattached…reattach them.
Remember….this is not a “Sherman Tank” don’t over tighten the connections.
Tight…tight………………too tight…broke!!!


Check the CCA free at auto parts store, dead condition leads to premature battery failure. You might try this if you are so inclined. Also check hood trunk, glove compartment, brake lights are turning off

I think the terminals are so corroded that the charger can’t even put a good charge to it.
Also, many times the cable will look good, but if you peal back a little insulation it’s all corroded under the insulation.


Thanks for the suggestions, I’ll head out after work and clean batt cables and connections.

Would a bad connection explain the voltage drop though, or maybe when a battery’s that dead, even just the normal parasitic car-off drains will make it drop like that when connected?

Many time, repeated attempts at turning the key energizes the cable enough that it heats up from the corrosion. Then one more try and the heated cable allows the current to pass and it starts.
Then because of the corrosion the charging system of the car couldn’t get the battery up to 13.5 volts.

I’m inclined to think that the voltage drop was just your technique in how you did your tests.


Ahh, another piece of the puzzle falls into pace. That makes a lot of sense, thanks.

You could have a bad alternator. Get your battery charged, it\f you don’t have a charger, take it to where you bought it and have it charged and load tested. Put it back in and go to a mechanic or auto parts store to have your charging system checked.

I agree with @oldtimer 11. Get the battery charged up and check out the charging system after that. Then check for a current drain on the system. Normal current drain on the battery should be less than 30 milliamps when systems are in the sleep mode.

+2 to oldtomer’s post. You need to have the charging system tested.

You may have a short in the big thick wire from the battery to the starter motor. Or the starter motor could be shorted out. There often is no fuse in that wire b/c it has to handle so much peak current. If this is the problem it’s a potential fire hazard, so be cautious.