New member - Thanks and alternator question

[fasteddie2015]

Howdy. Just picked up a 2015 Landcruiser (112K mi) to replace my 99 Lexus GS400 and 04 Tundra. Been using this forum to figure out if I have an alternator issue (13.4 to 14, fluctuates from day to day). Figure I should join since this forum seems to have the best LC 200 series info.

The mechanic I go to when I cant do it myself says alternator is fine unless it gets down to 13.2 or battery light comes on. This morning it hit 14 at fast idle right after starting. Battery stays at 12.5 overnight or even after a couple days sitting. Any advice is appreciated.

Main goal is that I dont want to get stranded with a dead alternator. Ever. Anywhere.

 

[Mogwai]

Welcome. Sounds normal, alternator cranks upon startup and lowers output as the battery warms. Lots of threads in here, some may be buries in "battery" threads though that revolve around why the alternator isn't the best charge source for dual-battery/AGM/lithium setups.

 

[bloc]

Plus, modern alternators are often designed to reduce their output when not needed to save fuel. I’m not certain if toyota does this but it has been common on other vehicles for over a decade.

As for being stranded.. toyota puts very very high quality alternators on their vehicles. As long as you don’t get mud in it I’d expect 150k miles minimum. More like 200 before I’d start worrying about it, personally.

I know my 80 had 270k on the original alternator when I replaced the brushes and the bearings and commutator were all fine.

 

[TeCKis300]

Normal. I echo what @bloc says.

Alternators these days are all "smart". In that they are tailored for specific battery types based on the required charge profile. They won't produce excess voltage once they sense a battery is topped off, and will only respond with more current output when they sense there is a load (e.g. heated seats). You'll notice the voltage is always generally very high upon start-up as it tops off the battery that has given juice to start the car. Then tapers off as the battery is sufficiently charged.

Benefits are that the battery state of charge (SOC) is well maintained without excess voltage overcharging batts (boils off electrolytes), requiring "watering" of batts that our fathers did regularly. Also saves gas by minimizing parasitic losses.

Smart alternators also impacts what @Mogwai touched on. Not your question, but alternators are not suited for alternate chemistries. Nor will they charge multiple batteries/battery banks as there's not sufficient charging voltage once they detect a full battery. Need a DC-DC charger for either of those things. Easiest upgrade strategy is a single larger battery, or multiple batteries wired together as a single bank so it appears as a single large battery to the alternator.