Ive got a few questions on the 42V (3 12V Lead Acid batteries).... Can they be charged up like a regular 12V with jumper cables? If not, is it possible I can have a list of everything I need to do to get it to a regular gas vehicle? Bypassing the hybrid system all together? Money isnt an issue im already deep in this hole.

 

It sounds like maybe your truck just has an engine start/stop feature?
If it is using 3 separate 12v batteries I would just disconnect them and charge each one separately with a standard battery charger.
The Key would be to disconnect them before charging since we do not presently know exactly how this system is controlled, and we do not want to burn up some discreet control module or something.
Treat it like a Doctors Oath DO NO HARM LOL

 

3 * 12V = 36V

3 * 14V = 42V.

As I understand it, it is 3X 7 cell (14V) batteries in series. They can't be charged with jumper cables.

 

Best I can tell the 2006 GM hybrid trucks were considered a mild hybrid and it was a retrofit but I could not find not many details online. I did see a video where it shows an inverter under the hood and cables coming up and mentioned an electric motor as part of the transmission.and it also stated that this was a factory "RETROFIT" The retrofit designation does seem to hint that it could be UN-retrofitted. I think that if you keep digging online you may possibly find someone whom has successfully removed the Frankenstein equipment on one of these, I seriously doubt that you are the only one considering it since it is looks like a huge amount of overkill for the addition of a start/stop system!. Good Luck man.

 

Have a solution for everyone with the “42v” battery issue. So as we all know the hv1255 are no longer in production for the public.
long story after real world testing

these are really just regular 12v lead acid batteries. So it’s really a 36v system I have tested and verified it

I removed the 3 batteries and modified the case to fit 3 batteries I don’t remember the bci code off the top of my head but their regular 12v lead acid 550ca 60ah each. I transferred all the connections to the new battery’s temp stents ect and it starts right up runs and drives fine no errors ect. This is not exactly a diy project there are physical modifications required and knowledge required about electrical systems, temperatures and PROPER VENTILATION

 

No they can't be charged with jumper cables

 

Everyone please report user "chima lecci". Makes useless posts to edit at a later date and include spam links. Check all previous posts, if you don't believe me.

 

I am trying to do the same thing with my 2005 GMC Sierra hybrid. Can you give details and maybe some pictures about the batteries used and the mods to the case where the hybrid batteriesnare stored under the back seat.

 

I have a 2006 GM hybrid truck; I have replaced the batteries and read 36v at the high voltage port. I have also replaced the battery under the hood. The three 12v batteries on the hybrid pack are all showing 12v each. I removed and individually charged them (revived all batteries but 1) 1 battery now is smaller 250ca it balances out to 36v at the business end + 12v under the hood. It doesn't even attempt to turn the engine. No errors shown on dash. No warnings from battery pack. I forced a warning by circumventing the 48v switch so I know its sending data to the ECU. The truck was functioning a few years ago but sat around for years due to a bad battery pack, the owner replaced them with new batteries (1 year ago) but 1 of the new old stock was 11v prevent it from working. This truck is in good condition other than this hybrid system and maybe old gas. I never saw it running so I have my doubts; maybe something else is causing it from turning over.

1- The square water cooled inverter upfront (under the hood - right hand side)... could it be causing it not to start? How does one check this? Can I force a bypass. How?
2- Since I have ZERO response when I turn the key and no errors I'm assuming some safety device is causing this. Is there a way to bypass low voltage switches on the truck to allow it to attempt to start?
3- Does the truck require that the main 12v up front also be 100% charged to start? I left the new battery connected with the bad battery for a few days after replacing (I didn't realize it was adding the 12v upfront to the total voltage on the battery pack - face palm GM). I charged it overnight last night and will try again this morning with the 1 small battery in the pack. I also I have the original battery revived 85% giving 12v this morning so I could put that back and try again.
4- What else can keep this truck from starting if all batteries are charged?
5- Anyplace I can measure voltage / ohms or check continuity? Any suggestions on how to test relays or other elements?

Suspicions. Could the total CCA be the issue? It would not make sense really, if a 48v system wants to see 48v is has that. It should attempt to crank the engine however sluggish. Right now I have two original Panasonic monster batteries and 1 smaller battery.

Please respond with technical info I have required experience.

Thanks in advance.

 

Can't solve your problem, but can comment on the following:

A lead acid 12V battery that measures 12V is at < 50% charge and is being destroyed being kept at < 100% charge.

CCA is an issue. Lower CCA results in bigger voltage drop, and less power.