Tundra alternator and battery problem northstar X2 27F 13.5

So I just had to replace my stock battery in my 2018 after 3 years. Which is expected here in the Texas heat. However, here is where things get a bit interesting, the first time I went to this local batteries plus where I got my first Northstar X2 27F in my 08 Tundra back in 2013 I bought the AGM cause I was running color shift halos, led DRLs, 12k winch, 900 watt system, etc.. Battery ran great for 4 years and then went bad. I brought it in cause 5 year warranty. We ran tests which indicated bad battery but also truck was putting out 13 ohm-m when I hit the gas slight bump to 13.3 ohm-m

Well anyways I knew the battery was bad and this guy was saying it is bad but you have a bad alternator. I’m said bullshit cause when I had to jump it prior times after an extended rest it would later get juice and start up first try. So the alternator was giving it juice.

After arguing he obliged and gave me a new battery under warranty but said I’ll bet you’ll be back in a month with this battery dead cause it’s your alternator not the battery. I’m like we’ll see. Sure enough the battery is going on 3 years and no further problems.

Now that I’ve stated that history, today I went in to buy a Northstar X2 cause he’s the only batteries plus with an X2 near me and once again we test the stock battery (mind you this is a completely different newer 2018 truck). Stock battery is shown to be dying. Same scenario. Overnight long pause and it loses juice. Turns over in the morning but struggling, after two 10 min drives this stock tundra battery gets juice and is good. Regardless I don’t want to end up stranded as it gets hotter here. I pull the trigger on another Northstar 27F X2 and we install it. Only to have the alternator in this newer truck show 13.5 ohm-m and even when I hit the gas 13.7 ohm-m. It never gets to 14 ohm-m. Same guy now telling me this truck needs an alternator or to get it checked. Long story short he has a point about alternator output it should go up to 14 ohm-m. But I’m guessing the Tundra normally puts out 13.7 ohm-m? Has anyone else run into this?? Thanks and sorry for the long winded post.

 

I believe AGM batteries require more voltage than the old style batteries. There is some difference, as you should not use a regular old style charger to charge them.

More info and possible fix for your issues here- https://www.tundras.com/threads/new-agm-battery-issue.67762/

post #22 may have the part to bump up the charge a bit so it works correctly with AGM, fixed the issue in the thread which is similar to your issue.

 

Never heard anyone refer to the voltage of an alternator output as ohm-m. But to your question…I brought our new GMC Yukon Denali back to dealer after first few weeks with what j though was a bad alternator. Frequently would see dash battery gauge in 12.x voltage range…verified with a multimeter. Turns out the computer varies voltage based on load and needs. And everything was indeed working properly. My gut feeling would be Toyota does the same thing?