I recently had toyota replace my alternator, however shortly before I got to the toyota dealership for the alternator I figured Id drop a new battery in hopes that I might not have to shell out for an alternator since my old battery was pushing 7 years in florida weather. I went to autozone and picked up a optima yellow top Group 35D
Lately I have noticed that when I start my car in the morning voltage is about 13.8 but after about 10 minutes of driving it drops to and stays at 13.0-13.3 volts and only getting to 13.6 if im on the interstate driving at about 2k rpms.
Do i need to worry about the lower voltage and should I look into a onboard charging setup? My apartment parking garage doesnt have any poweroutlets near my assigned space so a once a month charge from an external charger isnt really an option...
Thanks in advance

i would return the yellow top and go with northstar 31, you can fit 27f in stock location.

if you want to save a little, get the x2 from batteries plus, its a northstar brand, just rebadge for batteries plus store.
do online order and use coupon code, then do store pick up.

as far as voltage, its normal for 13.8 , a good digital volt meter should read at 13.4-13.8 at idle during cold start.

I second the X2 power from batteries plus (rebranded northstar). I got the 24F.

I paid $260 after tax and 20% off coupon from their website.

they installed it right there.

5 year non pro rated warranty sold me.

You can trick your alt-s diode to output slightly higher voltage, better for charging AGM batteries but they will still require a top off every once in a while if you don't go for long highway drives often.

There's an ebay option I've tried that works and I recently switched to the GM part number in the link below. It must be shaved down but works the same with a cleaner look installed.

Tech Center - Chi Town 4x4

Thanks for all the input, Ill have to look into that.
A concern I have with putting a larger battery in is that I also changed out my terminal connectors and when I did that, I shortened the battery positive wire a small amount to the point that it is stretching slightly to fit onto my current battery and I don't know that it would fit on a larger battery anymore... yeah kind of a big oops.
Would I be able to use something like NSi Industries | Easy-Splice™ 4/0 Kit
to extend the wire about 6 inches? I don't really have the time or the money to rewire from the starter to make the cable longer..

Keep in mind that AGM batteries such as Optima, require a higher voltage to fully charge than the standard batteries. Your alternator, while operating within it's normal range of output voltage, will not charge it completely.

I was using a trickle charger until I put this in, works well.

Dirty Parts

This dirty parts diode is the same idea as the $20 ebay part, or the $5 GM part. Boost that voltage!

Something like that won’t overload the system elsewhere? Like light bulbs or headlights?

Would I be able to install this GM part along with https://www.autozone.com/electrical-...-tap/32416_0_0 so that I could maintain the factory 7.5 amp fuse, essentially creating the dirty parts setup for ~ $12 plus shipping for the diode? Also will that diode affect any other systems? I have bad luck with headlights and would hate to have my new xenon depot system blow due to the change in volts, amps or current...

No need, the GM part IS the 7.5a fuse and diode all in one.

On a whim I tired this and it works, 14.7v at idle. 8.00 at the dealer for the diode.

You wouldnt have these issues, had you just gone with a Toyota battery

Yep, I even quoted Chi town 4x4 as a more reputable source for info than me! It works exactly the same as my ebay add a fuse diode thing which was more expensive. I kept it as a spare but if anyone wants the add a fuse/diode hodge podge $20 shipped. Or just go get a GM diode.

This must be what's happening with my DieHard Platinum AGM. It looks like there are several of you running the higher voltage without issue... has anyone had any problems with this?