Loaded up the snowblower to blow out the in-laws yesterday; left the Tundra idling about an hour and a half; loaded up blower to go blow out the business; truck idled about another hour and a half. Got back in; noted the nav screen/multipurpose screen was flickering. Turned off the truck to “reset/reboot” but when I turned the key, the truck (presumably) battery was dead.

Had to jump to get it going; drove home and fan speed would drop with engine speed when stopping at intersections; speedometer needle jumped around while driving; nav screen would flicker and turn off and on; battery gauge down around 9 volts. Got home and put on trickle charger overnight; haven’t yet checked this morning.

Is this a bad battery? Bad alternator? Something different? Not to cold out-in the 20s. Battery not quite 4 years old.

Any ideas? Thanks in advance!

Start it and let it warm up. With the engine running, pull a battery cable off. If it stays running, alternator is good.

Sounds like you have a bad cell. Usually they go to resistive state but in some case will short out.
Get a voltmeter and test from one cell to the other cell to find the bad cell.

Replace the battery.

It’s possible there’s something wrong with the battery and/or the alternator and it won’t charge the battery while idling. Letting it idle for 3 hours, all the electronics that were running plus the engine itself drained the battery. I’d check both the battery and alternator as well as your idle speed.

quote:

Originally posted by trapper189:
It won’t charge the battery while idling. Since you let it idle for 3 hours, all the electronics that were running plus the engine itself drained the battery.

This. At idle, the alternator can’t keep up with charging especially if peripherals are on (blower motor, radio, etc). It could be that it is a combination of bad battery and drain from extended idle.

quote:

Originally posted by David Lee:
Start it and let it warm up. With the engine running, pull a battery cable off. If it stays running, alternator is good.

This test may have applied to cars with generators in the 1950s, really dumb on a modern car. Without the battery in system, the alternator voltage can spike blowing electronics. MAINTAIN BATTERY CONNECTIONS AT ALL TIMES WITH ENGINE RUNNING!!!!!!!!!! Don't even momentarily disconnect as with a battery switch on a boat! If switching between banks of batteries, don't go past a disconnected position!

quote:

Originally posted by David Lee:
Start it and let it warm up. With the engine running, pull a battery cable off.

Absolutely not! This is a prescription for frying vehicle electronics and even the alternator, itself.

quote:

Originally posted by trapper189:
It won’t charge the battery while idling.

Maybe. Maybe not. Depends on a lot of variables, incl. alternator ratings and what's running in the vehicle.

bcereuss, sounds like you may have a bad alternator. Take the vehicle to a reputable car battery place or garage and have it tested.

OK..sorry about that. I did this to my Sienna without issue. Wont again. My battery was a 84 month in its 8th year.

That is a lot of idling, broken up by periods of driving which should top up the charge. Normal load at idling would likely be handled by the charging system, I'll assume heater blower was on high, which could have drawn more than the alternator puts out at idle. Maybe you shucked your belt, or the alternator is bad. I'd charge the battery, see if it starts and runs under more normal conditions.

Sounds more like a problem with the computer than the battery, have you tried rebooting the computer?

I think you're on the right track of battery or alternator, but don't have enough information yet.


If the battery takes and keeps a charge with your trickle charger (and that might take more than 24 hours if it was really low), then I'd be looking at the alternator.


If it doesn't take a charge after 24 hours, then a new battery is in order (that still doesn't rule out an underperforming alternator though).


Do you have an O'Riellys near you? I believe they should be able to test the battery and alternator without removing them from the vehicle and they'll do it for free.

quote:

Originally posted by David Lee:
Start it and let it warm up. With the engine running, pull a battery cable off. If it stays running, alternator is good.

If the alternator wasn't bad before, it will be when you're done. It might well go up in smoke. Don't do that.

As for the OP's problem, check in this order: connections, battery, alternator.

Buy a NOCO genius 10 if you don't have one. Charge the battery until it indicates green-full. Set it to the repair cycle (easy to do) lasts about 4 hours. These are NOCO's directions. About 100 bucks, maybe less if you find a sale. Doing this helped all my batteries.

quote:

Originally posted by Balzé Halzé:
Replace the battery.

This would be my bet.
Wife’s battery croaked in the 2019 4Runner. After jump start, electronics were going nuts. No cruise control, dash warning lights up the wazoo.
New battery and all was right in the world again.

My Tundra battery is going to be replaced soon. I don’t want to be out in the sticks stranded.

ETA: As egregore noted, the connections can mimic this too.

I checked the tender (Noco) and the battery does now (after overnight) indicate green (full). Didn't do the repair cycle; I'll see how it runs hopefully tonight or tomorrow. I'm thinking since the battery is four years old, that could be...but it might be the original alternator-so that is a real possibility.