# Positive battery terminal 'countersunk'? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [October 13, 2017, 2:12pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584 "2017-10-13T14:12:18Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![BillRussell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/billrussell/32/3179_2.png) [@BillRussell](https://community.cartalk.com/u/BillRussell)\ **Post date:** [October 14, 2017, 3:46pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/21 "2017-10-14T15:46:59Z")
I never ran across a passenger car with two 12 volt batteries. Can anyone tell me more? why two instead of one large one? How are they interconnected, just in parallel? ---
**Author:** ![sgtrock21](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/sgtrock21/32/246_2.png) [@sgtrock21](https://community.cartalk.com/u/sgtrock21)\ **Post date:** [October 14, 2017, 4:00pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/22 "2017-10-14T16:00:09Z")
Both my MGAs had two 6 volt batteries located behind the seats wired in parallel creating a 12 volt system. The only 24 volt vehicles I have encountered were military. I’m guessing this mystery vehicle’s batteries are switchable similar to dual fuel tanks. ---
**Author:** ![markg2](https://avatars.discourse-cdn.com/v4/letter/m/977dab/32.png) [@markg2](https://community.cartalk.com/u/markg2)\ **Post date:** [October 14, 2017, 4:00pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/23 "2017-10-14T16:00:46Z")
If I remember correctly, it was an option for our 1999 Suburban 4WD. We opted for a heavy duty radiator in addition (CO mountains). ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [October 14, 2017, 7:01pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/24 "2017-10-14T19:01:03Z")
Sliverado is a truck, and we have at least 1 with 2 batteries, oem, not added on. My bud had his 2nd battery blow up, So it may be like a starting battery and a secondary battery for accessories so as not to kill the starting battery. I would tend to believe the side post bolts are standardized, but a good question for a parts guy. ---
**Author:** ![PvtPublic](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/pvtpublic/32/13089_2.png) [@PvtPublic](https://community.cartalk.com/u/PvtPublic)\ **Post date:** [October 15, 2017, 11:28am UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/25 "2017-10-15T11:28:05Z")
Wouldn’t two 6v in parallel still be 6v but double the amps? Assuming both have the same amp rating. I think you meant two 6v in series to get 12v. ---
**Author:** ![markg2](https://avatars.discourse-cdn.com/v4/letter/m/977dab/32.png) [@markg2](https://community.cartalk.com/u/markg2)\ **Post date:** [October 15, 2017, 12:26pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/26 "2017-10-15T12:26:19Z")
The 1999 Burb was no where near that smart. The interior lights do not timeout and stay on until both batteries are drained. Our experience weekend before last and confirmed with auto parts. ---
**Author:** ![sgtrock21](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/sgtrock21/32/246_2.png) [@sgtrock21](https://community.cartalk.com/u/sgtrock21)\ **Post date:** [October 15, 2017, 2:16pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/27 "2017-10-15T14:16:15Z")
I’m sure you are correct. I have very limited electrician skills. The system was 12v positive ground. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [October 15, 2017, 5:43pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/28 "2017-10-15T17:43:14Z")
Trucks commonly have a factory option for 2 batteries One will be the main battery The other will be the auxiliary battery here’s some common uses for the auxiliary battery . . . light bar liftgate winch snowplow public address systems ---
**Author:** ![BillRussell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/billrussell/32/3179_2.png) [@BillRussell](https://community.cartalk.com/u/BillRussell)\ **Post date:** [October 15, 2017, 5:52pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/29 "2017-10-15T17:52:08Z")
How does the one alternator charge both? two diodes, so the lowest one gets charged first? ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [October 15, 2017, 6:39pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/30 "2017-10-15T18:39:05Z")
There’s typically an auxiliary battery relay Here’s a common one ![image](https://global.discourse-cdn.com/cartalk/original/2X/e/ea895717c3b1a009858ebcece98e7f11962ee7fd.jpg) ---
**Author:** ![bing](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bing/32/4619_2.png) [@bing](https://community.cartalk.com/u/bing)\ **Post date:** [October 15, 2017, 6:49pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/31 "2017-10-15T18:49:01Z")
So the answer is the guy didn’t have the correct bolt so used what he had on hand? On my diesel with two batteries, I’d service the connections about every year and replace the bolts to the post. Before I started I made sure I also had on hand the longer bolts needed where the two cables connect to the one battery. I’ve probably still got one left over some place. Personally though, I wouldn’t be very happy with having an allen wrench type bolt in there for fear of stripping it out trying to get it out again. ---
**Author:** ![markg2](https://avatars.discourse-cdn.com/v4/letter/m/977dab/32.png) [@markg2](https://community.cartalk.com/u/markg2)\ **Post date:** [October 15, 2017, 8:46pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/32 "2017-10-15T20:46:19Z")
I have zero knowledge auto electronics. I googled ‘install instructions auxiliary battery relay’. Frankly, it all looks like Greek to me. ~How much time would it take a competent mechanic to install the relay? Do you think the time for this procedure is defined and listed in the billable time vs. procedure standards that mechanics now use? ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [October 15, 2017, 8:49pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/33 "2017-10-15T20:49:34Z")
How did we get from possibly having the wrong bolt holding a battery cable on to relays. Even I could take a bolt off and put one on. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [October 15, 2017, 10:55pm UTC](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584/34 "2017-10-15T22:55:53Z")
I just showed a picture of the relay, because Bill asked how 1 alternator charges 2 batteries It was not meant as a suggestion or a solution to your problems, and I never said as much, for that matter [Previous page](https://community.cartalk.com/t/positive-battery-terminal-countersunk/108584.md?page=1)