# Wiring Common Alkaline Batteries in Parallel = voltage stays at 1.5v ? **URL:** \ **Category:** Factual Questions\ **Created:** [March 25, 2006, 1:40am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815 "2006-03-25T01:40:06Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [March 25, 2006, 1:40am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/1 "2006-03-25T01:40:06Z")
If I wire two or more batteries ‘in parallel’, am I only going to get 1.5 volts, but double the life/capacity? So, if the negative terminals are on the same connection (-) and the positive batteries are on the same connection (+) I get 1.5 volts for twice the life? Why I ask: I am a hobbyist. To start nitro engines in model cars and boats, we use a rechargable 1.5 volt ‘glow starter’ (uses a 1.5 v subC batt) that heats up the glow plug (like a spark plug). These things are terribly short on life, and people are always forgetting to keep them charged. Invariably, three guys are borrowing/killing one. Then I remebered an old set up I had from 20 years ago: It was four batteries line up in parallel (I think!). I always thought it was putting out 6 volts, but someone told me it was probably putting out 1.5 volts, but with the capacity of four D batts. Basically, this is month’s worth of starts and a season’s worth of backup starts. So, what is the scoop? ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [March 25, 2006, 1:44am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/2 "2006-03-25T01:44:48Z")
> [@Philster](#): > > If I wire two or more batteries ‘in parallel’, am I only going to get 1.5 volts, but double the life/capacity? Yes ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 25, 2006, 1:54am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/3 "2006-03-25T01:54:29Z")
For the most part, when you wire identically-typed batteries in parallel, the voltage is the same as one battery. You gain in two ways: 1. The energy capacity is greater. 2. The source resistance is lower. This is a fancy way of saying the paralleled batteries can source more current. Here’s what’s interesting: A “D” alkaline battery has about twice the energy capacity of a typical “D” NiCAD battery. But it also has a lot more source resistance. So if you’re going to put a bunch of alkaline batteries in parallel, you are primarily doing it to reduce the source resistance, and secondarily increasing capacity. So the real question is this: how many alkaline batteries do you have to put in parallel to have a low enough source resistance to make the glow plug work? I could look up data and do the math, but I’ve got to get home. ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [March 25, 2006, 1:59am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/4 "2006-03-25T01:59:46Z")
> [@Philster](#): > > If I wire two or more batteries ‘in parallel’, am I only going to get 1.5 volts, but double the life/capacity? You’ve got it right. > [@](#): > > So, what is the scoop? Hook up as many 1.5 v dry cells in parallel, i.e. all + connected together and all - connected together and you still have only 1.5 v. BUT as many times the current as you have batteries connected. If you only draw the same current as you would from a single battery then you extend the useful life by the number of batteries. OTOH conected in series the current is as one battery but the voltage is 1.5 x the number of batteries. Don’t do too many in series lest it be a lethal voltage. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [March 25, 2006, 2:24am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/5 "2006-03-25T02:24:14Z")
Yes, the voltage stays the same but the capacity is increased. The problem with parallel batteries is that they never discharge at exactly the same rate. So the stronger battery is continually charging the weaker one, in other words there are currents that circulate internally in the battery pack. This means that two batteries in parallel with not yield to the load quite twice the total energy of one. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 25, 2006, 2:41am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/6 "2006-03-25T02:41:38Z")
In principle, the previous posters are correct, _if_ the batteries are truly identical. If, however, they’re not (if they’re different ages, for instance, or different brands, or even just if a single brand with poor quality consistency), then the higher-voltage battery will be charging up the lower-voltage one, in an uncontrolled manner. This can actually lead to decreased battery life, or more extreme results like batteries heating up (possibly dangerously). ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [March 26, 2006, 8:45am UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/7 "2006-03-26T08:45:08Z")
> [@Philster](#): > > Then I remebered an old set up I had from 20 years ago: It was four batteries line up in parallel (I think!). I always thought it was putting out 6 volts, No, it was wired up in _series_, not 'i]parallel\*, if it was actually putting out 6 volts. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [March 26, 2006, 5:51pm UTC](https://boards.straightdope.com/t/wiring-common-alkaline-batteries-in-parallel-voltage-stays-at-1-5v/349815/8 "2006-03-26T17:51:41Z")
> [@Philster](#): > > Then I remebered an old set up I had from 20 years ago: It was four batteries line up in parallel (I think!). I always thought it was putting out 6 volts, but someone told me it was probably putting out 1.5 volts, “someone” was right. 6 volts will burn out a glowplug instantly. I used to make these up as a kid, as it was much cheaper to get flashlight batteries on sale than to buy a #6 cell, or the pre-soldered cox battery.