Thermo King Tripak Alternator issue.

First an apology for putting this in the FL section. It is just that I have an FL and couldn't see anywhere else to do this.
Just want to get a bit of input and see what everybody else has experienced.
I have a Tripak.
It is, I assume, the same age as the truck which is a 2007.
I ended up with the TK display unit throwing out an ALT error messages and shutting the thing down.
This ended up with a whole chicken and egg thing going on which I am still trying to solve.
I think I am almost there. The question is did the batteries kill the alternator or did the alternator kill the batteries? Or is it all one big coincidence?
You have to start somewhere.
A TK original new alternator is about $400. So I hit the internet and found a NEW replacement including shipment for $57.25. I was pleased.
So I fitted it and up she comes in the yard. All is working. I am happy.
Out on the road it gets interesting. All is ok, the unit fires up to charge the batteries but after a while the beep beep beeping starts from the truck indicating it is getting ready to shut down all auxiliary stuff like the sleeper lights etc.
Ended up with flat batteries a coupe of times one of which got expensive. Finally got out from under the load I was on and could concentrate on the problem. A quick trip to Tractor Supply Company followed.
I bought a battery load tester and checked all the batteries. 2 were incredibly bad and 2 were ok although slightly bulged.
So I replaced the 2 really bad ones with the only suitable 2 the store had. No more flat batteries and the APU is working fine but still after a much longer time the beeping starts again. I have to idle the main engine when this happens and after about 1 or 2 hours I go back to the APU. It is a good temporary compromise.
When I get out of Oregon - where there are no Tractor Supply Company stores - I am going to buy 2 more of the same batteries and eliminate that part of the equation.
So what is the problem?
The after market alternator is rated at 65 amp. I honestly thought that the original TK alt was that. Checking around I find that there are 90 amp alternators and even 120 amp alternators are being talked about. The 90's are readily available on eBay - German (quality) Bosch replacements.
I am going to have the original TK one rebuilt. The brushes are shot. However I am debating buying a 90 amp one on the cheap.
I think a 90 amp capability will eliminate flat batteries and allow me to run my fridge and microwave without firing up old faithful.
Thoughts? Input? Any ideas?
Many thanks in advance.

 

Great advice.
Yes you are right. Those nice new batteries I bought are taking up the slack right now even though the 2 originals were reading good. I do not trust them and they are for the chop. Best to change all 4 in one go but the store only had 2 Exide 31xhd's so I did what I could. Soon as I get out of Oregon I shall zoomed to the nearest TSC and get 2 more. That will be a good start.
The batteries we are talking about are Energizer AGMs which were purchased exactly 3 years ago in Sams Club. They were expensive ($1000).
When I removed the 2 bad ones the cases were somewhat bowed. I looked at the 2 remaining ones and they are the same.
I do not like that.
That is a sign of heat and over discharge.
They were all strained so to speak. Over a long period of time.
This is what makes me think that I have been over using the inverter. That the batteries were taking the strain because the alt on the TK couldn't keep up.
This is why I think of 4 new batteries and a beefed up alt.

Regarding wiring.
The inline 50 amp fuse was constantly blowing through 2016. No problem for 4 years then it acts out.
A big problem replacing it each time and I am not built for groveling on the ground in gravel parking lots anymore!!
So I replaced it with a 50 amp reset (bussman) brought up inside the sleeper. Originally used 12g because it was done in a pinch and I cannibalized the fuseholder.
That has all been redone. 8g cable, fuseholder removed completely, cables routed and tie wrapped properly.
I was an electrical engineering tech for 36 years so I am confidant when it comes to electrical work and the importance of correct gauge wire, connections and general rating of current etc.
When it comes to vehicle electrics though things can get strange especially when batteries are involved.
I think the 2 new Exides will be ok for a few more days. They are only maybe 5 days from the store. As for the 2 remaining energizer AGMs, they will be replaced with 2 more Exides exactly the same. So I will have 4 matching batteries.
The Exide CCA is rated at 950 below zero and 1025 at normal temperature. A good choice I think.

My question to you is this.
Do you think that the original TK alt was rated at 65 amps and that with 4 good batteries that is enough to run the house??
That this bowing I am seeing and the death of my alternator was all a coincidence or have I been asking too much of my system??
Bear in mind I live in my truck and run a microwave and a fridge. All on 110v ac from the inverter (a whistler 3000 watt)

 

Hmm interesting.
I do not think that is going to help though. Although I am always willing to admit that I am wrong.
If I start the APU and measure the voltage all I am doing is measuring the battery voltage, somewhat meaningless.
If I then disconnect the alternator lead and measure again on the same cable the voltage is bound to float upwards. The regulator inside the alternator will stabilize but without a load (the batteries) the current draw will disappear and the voltage moves upward.
I see what you are saying though. The only way to do what you suggest is to have a real substitute load. Not sure how I could do that or what I could use. Needs to be something completely stable, a battery is out of the question, too dynamic. Needs to be a resistor of some kind. Something that can handle some serious current.
What can I use?

 

Thanks to everyone for their input.
Further developments.
I ended up with a totally unrelated problem with the EGR. Spent way more time in a FL service center in Redmond, Oregon than I would have liked.
They had batteries at a very good price so although not matching the Exides, I bought 2 and completed the set.
Now I have all new batteries.
Eventually figured out what ASE tech/mechanic was referring to and was able to check.
The inverter has a digital display which reads the battery voltage. It was a nice simple shortcut.
With the engine shut off and no APU running you watch the loaded batteries start dropping from maybe 12.8/9 volts to 12.2 or thereabouts.
If you then start the engine the voltage will pop up to 13 volts plus !
Therefore when the APU is running to charge the batteries you would expect a similar voltage increase.
It doesn't do squat !!

So I found a function on the battery tester that I bought for checking the charging system and it also proved that the APU alternator is NOT charging those batteries.

I do not know if I have connected the wires to the alternator wrong - I do not think so - but I am certain that although that alternator is producing enough 'oomf' to fool the APU computer into THINKING it is charging it is in fact not doing diddly.
At this moment back in Mississippi the original ThermoKing alternator has been taken into a starter / alternator rebuild shop.
When I get back there I will refit it to the APU and I think all will be well.