# why not build cars with TWO batteries, for cold weather starting? **URL:** \ **Category:** Factual Questions\ **Created:** [December 31, 2003, 6:52pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979 "2003-12-31T18:52:29Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![disponibilite](https://avatars.discourse-cdn.com/v4/letter/d/5daacb/32.png) [@disponibilite](https://boards.straightdope.com/u/disponibilite)\ **Post date:** [December 31, 2003, 10:47pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/21 "2003-12-31T22:47:46Z")
And then of course you could buy one of those jump start things you keep in your trunk just for emergencies like you are talking about. I bought mine for about $50 at Sam’s Club a couple years ago. So far it has been very useful. Not just for me but for other people with dead batteries. Beats the hell out of jumper cables. Of course I live in Florida. Works fine here. How well one of those portable jump starters would work in Alaska I don’t really know. ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [December 31, 2003, 10:52pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/22 "2003-12-31T22:52:57Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*Yes, but how much did it cost you anually to _run_ this heater? A quick Google tells me these units run between 600 and 1,000 watts. If electricity costs you 20 cents per kilowatt-hour and you have a 1 kW heater and you run it 12 hours a day, six months a year, it’ll cost you almost $450 a year to run it. You could buy a a few batteries for that. \*\* You shouldn’t be running it 12 hours a day, particularly at home unless you really like to waste energy. Timers aren’t that expensive. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [December 31, 2003, 10:57pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/23 "2003-12-31T22:57:02Z")
> [@](#): > > \*Originally posted by dmartin \* > \*\*You shouldn’t be running it 12 hours a day, particularly at home unless you really like to waste energy. Timers aren’t that expensive. \*\* _I’m_ not, and in fact my numbers turned out to be conservative: > [@](#): > > \*Originally posted by robcaro \* > \*\*I used to run it about 15 hours a day and on weekends perhaps 24 hours a day. And, in Alaska, more than 6 months of each year. \*\* ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [December 31, 2003, 11:21pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/24 "2003-12-31T23:21:09Z")
When considering the cost of running block heaters, you can’t just look at the price of the electricity. Starting an engine at -25C (very run of the mill temp on a January morning here, not extreme at all) is very hard on the thing, because the oil is extremely thick at that temperature, and until the oil warms up there’s bugger all lubrication. Running a block heater greatly mitigates this, though naturally oil pan heaters are even more effective in this regard. However, oil pan heaters don’t assist as much in getting the car to start. So you can balance the price of plugging in the block heater against the increased maintenance and decreased auto life you’d incur by not plugging in. Many keep their block heaters on timers so that they run 15 minutes of every hour, or what have you, and at the least most people only plug their vehicles in before going to bed so they’ll start in the morning, etc. I leave mine physically plugged in all the time, but flip the breaker off so there’s no power to it. I run it overnight, or for 2-3 hours before going somewhere on a non-work day. Course, my car is an old diesel and flat out won’t start regardless of battery power in temps below -10C or so. ---
**Author:** ![donkeyoatey](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@donkeyoatey](https://boards.straightdope.com/u/donkeyoatey)\ **Post date:** [January 1, 2004, 12:49am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/25 "2004-01-01T00:49:08Z")
I’ve never seen them in a car, but I have seen many pick-up trucks with two batteries. ---
**Author:** ![SlickRoenick](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@SlickRoenick](https://boards.straightdope.com/u/SlickRoenick)\ **Post date:** [January 1, 2004, 2:46am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/26 "2004-01-01T02:46:46Z")
I remember our old station wagon had 2 batteries. I think i remember it being a diesel and my dad plugging it in during nighttime for the winter months. Also the old dump truck i used to do local deliveries in at the hardware store had 2 batteries in it, not diesel but gasonline. ---
**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:** [January 1, 2004, 3:33am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/27 "2004-01-01T03:33:07Z")
When two voltage sources are paralleled it takes some quite sophisticated control and monitoring equipment to make sure that they share the load. Batteries are never identical in voltage, internal resistance and state of charge. Paralleling them isn’t a very practical idea. ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [January 1, 2004, 3:57am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/28 "2004-01-01T03:57:33Z")
There’s been talk the last few years of cars switching to a 42-volt system. There’s so much electronic gear in cars today that 12-volts won’t be able to cut it much longer. ---
**Author:** ![5cents](https://avatars.discourse-cdn.com/v4/letter/5/46a35a/32.png) [@5cents](https://boards.straightdope.com/u/5cents)\ **Post date:** [January 1, 2004, 4:10am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/29 "2004-01-01T04:10:51Z")
Block heaters only need it plugged in for about half an hour, after that you’re just wasting electricity/money. Oil gets thick in the cold, so that’s why you use lighter weight oil in the winter - most synthetic 5W30 oils flow at -50F, some down to -70F. Dual batteries are a solution in search of a problem (except for things like RV’s, where you are running a lot of accessories). If you can’t get the car to start in the first 10 cranks or so, something is wrong (block too cold, fuel flooded, etc). Having more battery power at this point won’t help, and if you keep cranking, you’ll probably burn out the starter. Having said that, if the battery really is too small for the conditions you use it in, there are a few things you can do. First, you can try a battery blanket - these really do work. Second, if your engine compartment has enough space and your battery cables will reach, you may be able to find a slightly bigger battery that will fit. If you do this, please make sure the battery is held down securely and the terminals have adequate clearance with the hood (or other obstructions). ---
**Author:** ![donkeyoatey](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@donkeyoatey](https://boards.straightdope.com/u/donkeyoatey)\ **Post date:** [January 1, 2004, 4:18am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/30 "2004-01-01T04:18:08Z")
> [@](#): > > \*Originally posted by David Simmons \* > \*\* > > Batteries are never identical in voltage, internal resistance and state of charge. Paralleling them isn’t a very practical idea. \*\* Maybe there are applications where this is true, but every semi truck I’ve ever driven has had 2-4 12 volt batteries connected in parallel. Except for the Mack I drove many years ago that had four 6 volt batteries, two sets connected in series to get 12 volts, then those connected in parallel. When I blew up 2 of those attempting to boost the truck I got my first education on this subject. ---
**Author:** ![donkeyoatey](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@donkeyoatey](https://boards.straightdope.com/u/donkeyoatey)\ **Post date:** [January 1, 2004, 5:12am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/31 "2004-01-01T05:12:46Z")
And I should add that if you request a boost from a piece of heavy equipment you should be careful; every cat, hoe, buggy, rock truck and loader that I have run has had two 12 volt batteries connected in series (24 volt system). ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [January 1, 2004, 6:15am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/32 "2004-01-01T06:15:05Z")
> [@](#): > > \*Originally posted by 5cents \* > \*\*Block heaters only need it plugged in for about half an hour, after that you’re just wasting electricity/money. > \*\* Depends on the temperature. If it’s really cold (-35C, say), my car won’t start after a half hour of being plugged in, guaranteed. Not likely after an hour, either. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 1, 2004, 7:45am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/33 "2004-01-01T07:45:29Z")
> [@](#): > > \*Originally posted by Mr. Blue Sky \* > \*\*There’s been talk the last few years of cars switching to a 42-volt system. There’s so much electronic gear in cars today that 12-volts won’t be able to cut it much longer. \*\* Yes, the 42 volt systems are the future. As an intriguing aside, I note that the 42 volts refers to nominal **charging** voltage. 12 volts refers to nominal **battery** voltage. 42 volt systems use a 36 volt battery, but while 12 volt and 24 volt systems are commonly named by their battery voltage, what could be (and occasionly is) called a 36 volt system is commonly called a 42 volt system. This year, for the first time in a 30-year automotive career, I’m starting to see 12 volt systems being called 14 volt systems (their nominal charging voltage) instead. ---
**Author:** ![spogga](https://avatars.discourse-cdn.com/v4/letter/s/3ab097/32.png) [@spogga](https://boards.straightdope.com/u/spogga)\ **Post date:** [January 1, 2004, 12:30pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/34 "2004-01-01T12:30:23Z")
\*\* Gorsnak \*\* MINUS 25C?? Oh to be in England where -1 makes headlines ---
**Author:** ![notfrommensa](https://avatars.discourse-cdn.com/v4/letter/n/f14d63/32.png) [@notfrommensa](https://boards.straightdope.com/u/notfrommensa)\ **Post date:** [January 1, 2004, 3:25pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/35 "2004-01-01T15:25:11Z")
> [@](#): > > \*Originally posted by spogga \* > \*\*\*\* Gorsnak \*\* MINUS 25C?? > > Oh to be in England where -1 makes headlines \*\* I hope you meant -1 deg F. -1 Deg C happens several times all over the US, even in Florida. ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [January 1, 2004, 6:09pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/36 "2004-01-01T18:09:18Z")
> [@](#): > > \*Originally posted by spogga \* > \*\*\*\* Gorsnak \*\* MINUS 25C?? > > Oh to be in England where -1 makes headlines \*\* For your viewing pleasure, the long range forecast for [Saskatoon](http://weatheroffice.ec.gc.ca/forecast/city_e.html?yxe). Normal temps for this time of year are highs of -12 and lows of -22. Those numbers will dip a bit yet the next few weeks before they start to rise again. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 1, 2004, 6:41pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/37 "2004-01-01T18:41:07Z")
> [@](#): > > \*Originally posted by notfrommensa \* > \*\*I hope you meant -1 deg F. -1 Deg C happens several times all over the US, even in Florida. \*\* -1F (-18C)would be unusually cold for most parts of England even in the depths of winter; **spogga** was exaggerating a little; -1C wouldn’t really make the news. The UK is bathed by the Gulf Stream, which keeps the temperature a little milder in the winter than would otherwise be the case; Parts of Scandinavia sharing the same kinds of latitudes as us have winter temperatures that drop very much lower. ---
**Author:** ![The\_Great\_Unwashed](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_great_unwashed/32/4791_2.png) [@The\_Great\_Unwashed](https://boards.straightdope.com/u/The_Great_Unwashed)\ **Post date:** [January 1, 2004, 6:43pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/38 "2004-01-01T18:43:47Z")
> [@](#): > > \*Originally posted by notfrommensa \* > \*\*I hope you meant -1 deg F. -1 Deg C happens several times all over the US, even in Florida. \*\* No **spogga** meant celsius, but probably exaggerates, -1c ain’t headline news -10 certainly would be. I lived a while in MD, and extreme cold days used to confuse the hell out of me, because they didn’t seem _that_ cold – the thing we have this great winter humidity thing going where a mere -1c can suck the heat out of your bones. I believe spogga lives in Manchester, which is wetter than Venice. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 1, 2004, 6:54pm UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/39 "2004-01-01T18:54:50Z")
> [@](#): > > \*Originally posted by The Great Unwashed \* > \*\*I believe spogga lives in Manchester, which is wetter than Venice. \*\* The canals are not quite as picturesque. ---
**Author:** ![5cents](https://avatars.discourse-cdn.com/v4/letter/5/46a35a/32.png) [@5cents](https://boards.straightdope.com/u/5cents)\ **Post date:** [January 2, 2004, 5:40am UTC](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979/40 "2004-01-02T05:40:01Z")
> [@](#): > > \*Originally posted by Gorsnak \* > \*\*Depends on the temperature. If it’s really cold (-35C, say), my car won’t start after a half hour of being plugged in, guaranteed. Not likely after an hour, either. \*\* I’m a canuck in exile. Cleveland doesn’t get too cold - nobody even knows what a block heater is. But I have lived in places where it does get very cold. -35C is nothing :). Try -45C… [Previous page](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979.md?page=1) [Next page](https://boards.straightdope.com/t/why-not-build-cars-with-two-batteries-for-cold-weather-starting/221979.md?page=3)