Car keeps losing battery power 100% while battery is fully charged

About a month ago my highlander lost battery power and I noticed that there was a door left open. Got a jump from insurance guy who said battery was fully charged when he hooked up to give me a jump. The car started right up and I thought that was that.

A few days later while we were driving the radio kept losing power though the car kept running without issue. I checked the battery to discover that the positive side terminal connector could be rotated slightly, so I tightened that up and figured all was well - until it happened again. All power gone, no dash lights on with key on & door open.

Read an article on the subject here (older Cadillac I think) and took the advice to clean the battery terminal, so I took off the wires, filed down the terminal connector so that it was clean and flat. The 2 wire connections on the hot side were a bit rusty, so I put a little grease on those surfaces to make sure they’re making solid connections. Since it was rustier than I expected, I figured this must be it - until it happened again today - about a week later.

I turned off the car and was back to the original complete loss of power for anything in the car. I banged around the ignition and slammed the door to see if this would bring back power, but nothing. So I’m sitting there thinking and then the power comes back on once again and everything looks fine.

Fortunately we’ve not been stranded, but it’s only a matter of time I expect and sure would like to get this fixed once and for all.

Thanks in advance,

Year/miles on Highlander? Battery age?

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Did you clean them before you reattached and then greased them? Grease is not a conductor.

More info about this car would very useful… like, Do you live where the roads are salted in the winter? How old is the car? Miles?

I didn’t clean them. I thought the grease would stop the rust as it was all just light surface rust. Didn’t realize that grease wasn’t a conductor though.

I thought the car info I provided came through. It is a 2005, 160K miles. I live in Arizona, so roads aren’t typically salted.

If the battery is over 5 years old, have it tested.


It may be AZ but there is still the possibility of corrosion. You clean, wire brush, reattach and THEN grease the joint.

Have your battery tested. Have the resistance of your battery plus and grounds tested, too.

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It’s a 2005, 160K miles. 4 year battery purchased in July 2019.

It’s not qute 4 years old - July 2019.

Still have the battery tested.

Heat kills batteries.


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Thanks for the procedure.

Do you know if Napa or another regular parts type store will test the battery & grounds as you suggest, or would I need to go to a mechanic for that?

Some parts stores will test the battery for free.


Thank you. Do you think Napa or regular parts store will suffice to do the testing?

Okay, I’ll get the battery tested. Thank you.

Mechanic for that. Parts store employees are not mechanics, they are salespeople.

Thank you.

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Do you think a batter tester like the one below would properly test as needed?

Why buy something when most Autozone stores will test your battery for free . And if you need one thier prices are in line with most places and they might install it for free.

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That’s a conductance battery tester.

Conductance testing is the latest technology in battery testing.


Thanks I’ll check it out.

Arizona-car, battery close to 4 years old, hmmmm … I"m guessing you have two problems. Battery starting to go on the fritz, and imperfect wiring harness connections at the battery. If you know how to work a volt meter, a simple test, before first start of the day the battery should measure about 12.6 volts, then immediately after starting the engine, 13.5 - 15.5 volts. Probe the battery posts, then compare to probing at the connectors. Shouldn’t be much difference between the two