_94fleet Posted January 29, 2018 Report Share Posted January 29, 2018 not car audio related but the batts in my 07 duramax dont nave enough juice to crank. i removed them and let them sit for 24hrs and the resting voltage is 12.7 and 12.6. can i have bad batteries even tho the resting voltage is fine? they were fine until it started getting cold. B2 Zero.7r - Soundqubed 4-120 - Digital Designs 9918 - Rockford Fosgate T1 5.25" - Deh-80prs - XS Power D3400 XS Power XP3000 - Mechman 250A - Big3 Link to comment Share on other sites More sharing options...
reedal Posted January 29, 2018 Report Share Posted January 29, 2018 what does the voltage drop to when you crank the engine? SMD Tool Map https://www.stevemeadedesigns.com/board/topic/193176-smd-tool-map-new-november-2014/ Build log https://www.stevemeadedesigns.com/board/topic/197217-reeds-03-tahoe-hat-sqaq-singer-xs-shca-cockbox-80prs/?page=32 Link to comment Share on other sites More sharing options...
_94fleet Posted January 29, 2018 Author Report Share Posted January 29, 2018 all i have is a cts2 and it says 11.8. i understand these are 12v batts. if that makes them bad im ok with it. just dont want another thing to be killing them and im running thru batts. B2 Zero.7r - Soundqubed 4-120 - Digital Designs 9918 - Rockford Fosgate T1 5.25" - Deh-80prs - XS Power D3400 XS Power XP3000 - Mechman 250A - Big3 Link to comment Share on other sites More sharing options...
ShadeTreeMechanic Posted January 29, 2018 Report Share Posted January 29, 2018 The only way to know for sure if the batteries are good is to load test them. It is possible to have a bad cell that will charge but not deliver the current. It would only take one of the batteries going bad to cause a problem. Normally the cranking voltage should be above 9v but with two batteries in parallel, you could still have a bad battery. They would need to be tested individually to know for sure. You could take them to a place like AutoZone and they will test them for free. You should check for other possible problems in the battery cables and their connections, one bad connection could be a show stopper. Often times the battery cables are hardly big enough to start the engine when its warm. I have upgraded all of the cables on my diesel with 3/0 welding cable and it made a huge difference. Does GM still use the side terminal batteries? These provide a marginal connection at best so they have to be super clean and tight. If you can move any connection by pulling on the cable then it is not tight enough and some times the side terminals won't get tight enough no matter what you do. Take apart all of the connections and clean them with a wire brush and apply some dielectric grease to them when you put them back together. Then move on to the starter. If there a problem with a battery or connection that causes it to crank too slow to start, the starter will build up a lot of heat that will damage it. Its not uncommon to have a starter that still cranks but it is so hurt that it will never crank fast enough. I have seen a bad battery cause the starter to burn out this way and I have done it myself. I think this truck should have a block heater that should be plugged in overnight, especially if you run summer weight oil year round. I have an onboard trickle charger on my truck that is plugged into a splitter with the block heater. This way the batteries are getting topped up overnight. Sorry that's a lot to read, I have the day off and I am on my fourth cup of coffee. lol give everything a once over and let us know what you find. 91 C350 Centurion conversion ( Four Door One Ton Bronco) 250A Alternator (Second Alternator Coming Soon) G65 AGM Up Front / Two G31 AGM in Back Pioneer 80PRS CT Sounds AT125.2 / CT Sounds 6.5 Strato Pro component Front Stage CT Sounds AT125.2 / Lanzar Pro 8" coax w/compression horn tweeter Rear Fill FSD 5000D 1/2 ohm (SoundQubed 7k Coming Soon) Two HDS315 Four Qubes Each 34hz (Two HDC3.118 and New Box Coming Soon) Link to comment Share on other sites More sharing options...
_94fleet Posted January 29, 2018 Author Report Share Posted January 29, 2018 ok thanks. yea they are side terminals. i will look over everything again. chances are i will replace them B2 Zero.7r - Soundqubed 4-120 - Digital Designs 9918 - Rockford Fosgate T1 5.25" - Deh-80prs - XS Power D3400 XS Power XP3000 - Mechman 250A - Big3 Link to comment Share on other sites More sharing options...
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