Using lifepo4 in a petrol car ? Which one ?

[croustibat]

Hi guys !

I have been looking for infos on these batteries for some times now, and it looks like i found a nice source of informations here.

A bit of background before starting; i am in my 33years, am an engineer by heart and by qualification, although more in the computer science domain.

I also have some hobbies, like going faster in a 10K€ car on tracks than most ferrari/porsche/other exotic and expensive car drivers. And i have been quite succesful on that one The key being to consider you just drive a pile of metal that may end its life in a tire wall or on its roof on the next corner. This mindset is hard to attain for people that drive 200K€+ cars.

My 10K€ toy -cant really call that a car- is an old 1992 nissan. Americans know these as 240sx s13, however in Europe we have it as a 200sx s13, and it comes turbocharged from the factory. Meaning it is easy to get more power ! I stopped a bit over twice the power it made when it was new. Some dont... these engines are quite surprising though. The highest reliable known one outputs around 700HP . I think 350HP is enough in a 1000kg(2000lbs) rear wheel drive car with absolutely no driving assist.

Now, as a toy, it does not get used often, and frankly i am tired of killing lead acid batteries when i just forget about them. That and they weight a ton and a half, and use too much room; i need to remove a lot of parts to remove it.

And here comes lithium iron batteries. They seem to be exactly what i am looking for: small, light, lots of life cycle, low discharge rate, and SAFE. Yes, i already transformed an RC helicopter into a fireball due to failing lipos, so i do not want the same to happen to that car. Even more when it has alcohol based fuel near it. Oh, and me strapped in a bucket seat just a meter away, too.

I understand this forum is not exactly about using batteries to START petrol engines, and more about powering whole cars or bikes, but maybe you can help me make an informed decision, or find my dream battery ? I found infos about these batteries on bikes, skidoos, but not cars, so i was wondering why. I have some electrical and electronics knowledge, but not as much as i would need.


Basically, here are the problems:

-I need 12V 150A, probably 200A peak discharge to start the engine. It is a 1.8L 4 cylinders with low compression engine, so it does not start immediately, and it has sticky oil, so it always takes some turns to start, and the first ones are quite hard on the starter motor. The battery needs to cope with that.

The car vibrates quite a lot; engine is hard mounted. Do i need to make some soft mounts for the battery ? Padded cells in a box would be enough ?

As it will replace a lead acid battery, it will be part of the charging system, meaning the alternator will keep a voltage of 13.4/13.8V max. Do i need overcharge protection ? How do these work ? Do they just cut off the battery, or prevent it from charging ?

I need power in the car for various devices, like ECU, fuel pump, ignition and injectors system. While the alternator can provide enough, the less it provides, the less power it robs.

Considering all that, should i even go lithium iron ? I was thinking a 4S3P (7AH) or a 4S4P (10AH) would be enough, but is it ? 4S4P are supposedly enough to start a rocket 3 engine (3cylinder 2.3L engine from triumph-yes, it is on a bike), so it should power my puny 1.8L.

I also did not find many infos on manufacturers. Saw earthX, that include a BMS in their battery pack, but they get quite costy and they just look like regular chinese batteries. Saw ballistic, and does not look like they even have a BMS. Then there is shorai, which use prismatic cells, but lies on the specs (they use "lead acid equivalent", thus marketing 7AH batteries as 20AH ones). The price is even higher.

Which leads to another question: regular,cylindrical cells, or prismatic cells ? I heard that prismatic is better, but it looks they dont like vibrations at all.

I see a lot of people here are building their own kits from A123 cells, but i would rather not do it myself. I do know my limits. Are there some people here that could do it ? Budget wise, the aim is to keep near / under the price of a race battery, which is around 200$ / 150€ .

I am also closely working with a tuning shop that may be interested in distributing these batteries, but they first want some proof that it works before deciding anything. They currently sell "race batteries", aka small lead acid ones that will die quickly due to being discharged too much on each start.

My toy is usually a test mule for them, so i guess it will be one more time

Thanks for reading all that. So, what do you think ?

 

[John in CR]

Voltphreaks has racing batteries, but they're crazy expensive to me http://www.voltphreaks.com/products_street.php.

Personally I'd just build my own using series blocks of 4 to 6 in parallel parallel A123 26650M-1 cells in series. If the alternator really puts out 13.8V max, then you'd be golden just checking for balance before each race. I've got a bunch of M1 cells, so I wouldn't get scientific about it. One for sale would require a BMS though. I question the alternator max voltage though. Just because a lead battery doesn't go higher doesn't mean anything. They shed heat instead of going higher.

 

[croustibat]

Thanks for reply. I am not doing competitive racing, just doing trackday events. This allows me to run unlimited mods -bar security ones- which lowers global costs, and is still very fun.

Voltphreaks looks like a total ripoff to me. 700$ for a 11AH "lead acid equivalent" ? Thats means a mere ~4AH real capacity ? no way.

The alternator has a built in regulator that limits voltage. When that thing goes, the voltage can go up to 17V.

Fortunately i have a sensor and an alarm on that; logs tell me that when engine is running, the voltage is between 13.5 and 13.8V ; should i take that voltage for the "true one", or is it a false reading due to the dead battery being connected ? This is somewhat the limit of my electricity knowledge The battery is really dead, it reads 0V when engine is off. Even if i just drove 50km, in less than 10seconds voltage drops to 0. I got a battery booster but it is on its way out too ...

I am not very fond of building my own battery TBH. I dont trust my welding skills enough, and not really sure it will cost less than a K2 battery for example, which is supposed to be using the cells you are talking about and a BMS (but i did read that bms had no overvolt protection, meaning it is useless to me - also these connectors are wayyyy to close and thin for my taste). And has a warranty on it.

If i used A123 M1 cells, would 12 be enough ? Or should i go with 16 ? 16 would give me 12V / 10AH, which i think is enough; but if i can get away with 4 less cells, then i'd do that.

On another note, what if i use 4 A123 20AH pouches ? 120$ for pouches, then needs BMS and casing. If it really is 20AH and not yet another fake rating, and the assembly is not that hard, maybe i could go with that. light and small 20AH battery is good enough for me, i dont need the ultimate weight reduction battery either( FRP doors and hood and lexan windows have a better cost/weight ratio that and i would be driving a caterham, not a nissan ). But i do need a small sized battery.

 

[John in CR]

I talked to my Chinese guy and he suggested going without a BMS as long as the voltage coming from the alternator isn't exceeding 14.4V . If you're not running the radio and lights when you're parked, then your battery doesn't need much capacity, because it's running everything off of the alternator. eg Normally you start the race and end the race with a full battery, so the battery hasn't supplied any net energy. In your current case, you get a jump start of your dead battery and end the race with a dead battery, so it didn't supply anything either. Actually the dead one is a net negative, because while running the alternator is continuously trying to charge it and that energy gets turned into heat and maybe a chemical reaction too instead of being stored.

He said he ran his diesel SUV for over a year with a 5ah12V battery and killed it by leaving the lights on with the engine off. The reason he said no BMS is because to handle the high peak current during starting requires BMS's that are just too expensive. Instead just check balance once in a while...maybe when you check the oil. He recommended 3 different routes:
1. He deals in an 8ah cell Lifepo4 cell that he can get that will deliver 160A continuous 500A pulse.
2. The A123 20ah cell
3. 2 in parallel of the Headway high power cells.

If you know you're getting new grade A A123's, they're the best cell of the bunch, but there are ???'s about the grey market cells available. My guy won't touch them, because at this point in time you don't know what you're getting, and some of those made in USA A123 AMP20's are defective. Another problem is connecting them, which for your use and high current pulse demands requires proper tab welding. If you can make the tab connections, then making the battery with the 4 cells in series is simple...just clamp them between 2 pieces of lexan for some compression, seal around the sides and you've got a battery. Those cells are only 7mm thick and weigh about a pound each.

Being cylindrical cells the Headways don't need compression. They bolt together and holders are readily available, so putting a battery together is simple, and then put them in some kind of plastic box, say a cheap small tool box. They're a lower power cell, so you'd have to buy 8, making them the higher priced option, but it does give you more capacity like you wanted, though I believe unnecessary.

His 8ah cell also bolts together. It's a rectangular cell 19x80x140mm, so your car battery could be 3"x3.15"x5.5" and weigh under 3 lbs with the 4 cells wrapped together with duct tape. I've had similar shaped Lifepo4 cells bulge a bit despite the aluminum case, so it's a good idea to compress them some too along that broadest surface. They're about $25/ea plus shipping from China.

He doesn't want to deal in assembled packs, because they're getting more and more difficult to ship. He doesn't deal in the Headways or A123's but there are other sources around. If you're interested in the 8ah cells, I'll put you in direct contact with my guy.

John

 

[croustibat]

The alternator will always apply some voltage though; wouldnt it be similar to try to charge the battery all the time, like overcharging it ?

I still need more info before deciding what to do, as i am currently waiting for some rose joints to be delivered, so the car is not going anywhere for before end of february ... I didnt know there were 8/10/15AH prismatic cells though. May be worth it.

One basic question : if i wire 2 cells in parallel, i double the capacity and keep the same voltage. But do i also double the max discharge current ?

 

[dnmun]

the problem is that as the lifepo4 cells go out of balance then some will be at low voltage so that as the charger puts out a voltage that would bring all cells up to the same voltage but in reality some will be low and that causes some of the cells to overcharged, which kills them. then when you discharge there is nothing to prevent the low cells from overdischarging. you should stick with SLA imo. real batteries cost real money and cheap stuff without protection is just money down a rat hole.

 

[croustibat]

Which means i need to balance them on a regular basis, and no i am not using a lead acid battery again. I need to remove my front bumper, support bar, intercooler and half the intercooler plumbing to just remove the battery, and i cant fit a smaller SLA one.

 

[John in CR]

Lifepo4 is much more tolerant of not being balanced up at the top of charge. It's running a cell out of juice and continuing to draw current through it from the other cells that it doesn't like. For at least a couple of years Thundersky recommended a cutoff voltage of 4V/cell for their Lifepo4's.

Think of voltage as pressure, so once battery voltage equals max voltage from the alternator then no more current can flow. I'm not up on car electronics, but I've seen cheapie low current lead chargers whose current falls almost to nothing at 13.5V, but only almost. They can't be used to charge lithium batteries, because that voltage will creep up to around 17V. It doesn't with lead, because as long as it's a trickle of current, the lead battery just sheds the energy as heat and voltage goes no higher.

With your battery so hard to access you'll want to do a few things so you don't have to get up in there for a long time.
1. If the car doesn't want to start, don't keep cranking it over until you run the battery, or leave your lights on, or anything else that would run the battery all the way down. Self discharge rates are very low, but If leaving it parked for a
long time (over the winter or whatever), look out for small current draws on the battery....The clock in the car stereo etc.
2. Run a 5 wire balance and monitoring tap off the battery to somewhere easily accessed.
3. Check it more often than I would. Mine is easy to access, and I know myself, so after checking it a few times in the first week or 2, that would turn into one every few months.

If you wanted to avoid checking, then pick up 5 single cell lifepo4 chargers, one as a spare, and wire them up to be able to plug to the 5pt plug above and connect it overnight once a week or once a month or before race days, etc. You're won't be drawing the charge status down low like we do with our ebikes. It's over-discharge that you're concerned about, and with A123's for example, 3.45V, 3.5V, 3.65V, 3.75V, and 3.8V are all the same thing...full. Just a split second of discharge and a cell sitting at 3.65 will be at 3.45V. There's just almost no energy in the surface charge.

Many guys get way to anal about balance of lifepo4. Some of the cells will lose their ability to hold the surface charge over time anyway. That means you could have just used your single cell charger to charge each cell up to a perfect 3.65V, disconnect it and come back an hour later and a couple of the cells are only at 3.5V . That would be almost meaningless. What would be meaningful is after a fresh balance and you turned the car over for a few seconds, and then checked balance. As long as they're all near equal voltage and above 3.3V, then you're fine. The few tenths of a volt between 3.0V and 3.4V is where the meat of the lifepo4 capacity lies, and until you get down near full discharge of the lowest capacity cell, once the surface charge is burned off, at rest healthy cells will stay in that same narrow voltage range.

John

 

[Hillhater]

If you are looking for a lightweight, cheap, LiFePo4 starter battery,..
..you could consider trying these..
http://www.hobbyking.com/hobbyking/store/__14074__ZIPPY_Flightmax_8400mAh_4S2P_30C_LiFePo4_Pack.html
250 A continuous, 330A peak, and only $76
They have been used on big 4 cyl bike motors, so no reason not to start a car. ?

A more "conventional" LiFePo4 , 12v solution would be the K2 pack at $350..
http://store.peakbattery.com/k212lfpba.html

 

[dnmun]

"Thundersky recommended a cutoff voltage of 4V/cell for their Lifepo4's"

thundersky does not use stoichiometric lifepo4. they add yitrium from what i have read and it allows them to spec a charging voltage of 4.2V/cell. i don't know if they would recommend you not use a BMS either. but of course they are only a battery manufacturer.

 

[John in CR]

Please do explain how a 4 cell lifepo4 pack with healthy cells that is bulk charged to 13.7V and is never deeply discharged will get out of balance enough to damage cells from an out of balance condition resulting in over-charging. It's a very low % possibility with only very occasional balancing, and even if you found a capable failure proof BMS it would cost more than the battery anyway. Plus we all know that BMS's cause more Lifepo4 failures than anything else.

Unlike lead battery explosions, which are far more common than people realize, and RC Lipo which the OP already knows are fire prone, Lifepo4 fires are all but non-existent other than shorts circuits, BMS failures, or defective cells (which is why I wouldn't touch A123 amp20's for a car, since a failure that releases 20ah in a short time is bound to create an event).

The only BMS managed packs that I'd trust are those on Zero emotos, and I put little faith in manufacturers otherwise. Look no further than some of A123's lunacy or more recently Boeing's supplier for the packs in the Dreamliner.

John

 

[croustibat]

If you are looking for a lightweight, cheap, LiFePo4 starter battery,..
..you could consider trying these..
http://www.hobbyking.com/hobbyking/store/__14074__ZIPPY_Flightmax_8400mAh_4S2P_30C_LiFePo4_Pack.html
250 A continuous, 330A peak, and only $76
They have been used on big 4 cyl bike motors, so no reason not to start a car. ?

A more "conventional" LiFePo4 , 12v solution would be the K2 pack at $350..
http://store.peakbattery.com/k212lfpba.html

I checked these one, and i seriously considered the hobbykind one. But it seems the 30C rating is faked, and it is more a 10C rating. Someone here tested it and was not that impressed, there is a thread about it in the battery section.
That is the cheapest and simplest solution i could find by far, meaning something had to be off :?

Big 4cyl bike motors are only 1.3L / 1.4L, and they dont have heavy moving parts like my engine has (turbo engines are the opposite of high revving NA engines, the internals takes a massive beating with the pressure, whereas NA has trouble with piston speeds meaning they mostly need tight tolerances and light parts), nor a heavy transmission. I may give it a try though, if i can get more returns on it. Or if hobbyking warranties it correctly, as it is the simplest route. I am a bit afraid of the wire diameters though, but maybe i am just chickening out.

As far as overdischarge goes, my car currently has an alarm and a stereo, and both are going to be removed. The alarm is useless as the battery is always drained out, and the stereo is useless as the car needs earplugs to be driven.

It also has a "you forgot to switch the lights off" buzzer, which helps.

But in any case i plan to use a FIA approved cutoff switch to make sure there is no drainage.

As they are tiny batteries and not dangerous, i planned to mount it in cabin, behind the dash, near the firewall. The car is RWD meaning the battery will have shorter starter and alternator leads there, and it allows me to mount a very short wire to the cutoff switch too.


I will check the story of dreamliners right now too. Thanks.

 

[gensem]

I would be more inclined to get A123 20ah pouch cells and not lifepo4 from HK.

You can make a 4s 20ah pack with 6-8awg discharge leads (depending on your needs) and JST balance plugs (for balancing with a RC charge) fairly easy.
check this out
http://endless-sphere.com/forums/viewtopic.php?f=14&t=38545&start=600#p646501

But if you are not familiar with that, you may aswell ask cell_man to do it for you.

 

[matt20]

Well, I'm no expert. I wanted to do something similar for a RV cabin battery. I built a 80 amp hour battery using these:

http://evsource.com/tls_lithium_calb.php

I connected 40 amp batteries in a 2p4s configuration. I used the top balancer between the cells:

MiniBMS Cell Boards http://evsource.com/tls_cleanpower.php

So far it seems be getting charged by the alternator. I am using it on my maiden voyage to the west coast. So far, it seems to be working OK...

Here is someone that did make a conversion without a bms and it seemed to hold up for a few years...

http://www.youtube.com/watch?v=m1blV9LaH44

Matt

 

[croustibat]

I didnt think about the alternator current. If it really applies 30A, i have to use cells that can take that as a charge current :?
But maybe this is due to his battery having a very small capacity ? 2lbs mean it should be around 5 ot 7Ah...

As far as calb go, their smaller cell looks to be 40Ah, and that would really be overkill for what i want to do. Thanks though

 

[croustibat]

Ok, some news ...

i am NOT going the HK route.

That battery is on backorder everywhere ... except in the nearest warehouse from my house, and it is in the UK. Meaning as i live in France, no custom duty or anything.

They even offered me a 10% discount on the 8.4Ah battery ... and then told me they cant ship it from UK, that i had to get it from the international warehouse. Where they dont have it, of course.

Of course i contacted the support to get an explanation, and everything i got was "i am sorry we cant, order from somewhere else". That is not the answer i am waiting for when i ask "why" , and i certainly cant see why. Even if the UK has restiction on air shipping, ground shipping is still ok. And this is BS as i already got many heli parts and batteries from the UK in the past...

and then i saw the video of someone starting a car with it. Sure it starts, but voltage drops to 10V during start ... not sure they will live for a long time.

So HK is a clear no. Too bad, it was the easiest solution... I think i'll go with some 20A pouches. I still dont know wether i get a built one from cell_man or do it myself ... a 4S1P does not look that hard to do, but if i just save pennies by building it myself, there is no point.

Thanks people :wink: I will post the results when i am finally decided and when the car starts with some cells

 

[Lebowski]

As far as I know modern sport motorcycles already get a lifepo battery fitted at the factory, and they are for sale on the motorcycle aftermarket for retro fitting to older motorcycles... have you looked at motorcycle batteries ?

 

[croustibat]

Yes I did. They are mostly using ballistic and shorai products, which is quite overpriced compared to what i can see here.

 

[Hillhater]

Ok, some news ...

i am NOT going the HK route.

That battery is on backorder everywhere ... except in the nearest warehouse from my house, and it is in the UK. Meaning as i live in France, no custom duty or anything.

They even offered me a 10% discount on the 8.4Ah battery ... and then told me they cant ship it from UK, that i had to get it from the international warehouse. Where they dont have it, of course.
....
and then i saw the video of someone starting a car with it. Sure it starts, but voltage drops to 10V during start ... not sure they will live for a long time.

HK are a pain to buy from..even with a local W/house.
Sometimes they ship Lipo with false contents and valuation to avoid customs charges etc... other times they delay shipping for weeks with no sensible explanation. :x
you need a friendly ES member in the UK to act as a "mailbox " for you... :wink:
that 10v reading under load should be no worry, LiFePo4 cells can sag hugely under high loads, but its not a problem for "burst" loading.
PS : do you know what the voltage is on a 12v Pb battery when starting a motor ?
.. But at that price ..i would have used a pair in parallel anyway. !
good luck with which ever solution you decide.

 

[FastDemise]

My experience with LiFePo is I made myself a simple 4s16p A123 18650 cells battery for my small 1980 Honda CM400T. It's crazy overkill in size but fits the stock battery compartment perfect so I'm not complaining. I have been using it for 3 months now and only charged it twice on my balance charger. Both times it was not necessary as my Cellpro noted only 5mV difference at worst. I love the added brightness of all my lights getting a full >13V at all times. I am planning on splitting up the pack so my roommate can use the 4s8p pack on his KLR650. I wish you luck on your car. I myself want very badly to make a pack for my Jeep Cherokee and have a few capacitors to offset the initial starting draw to allow me a very small battery to just maintain charge when not in use.

 

[croustibat]

So, a bit of update.

I got an OSN 4S4P battery, A123 cells (approx 10AH). I have to say nancy/april has been very reactive and gave some good advices. I will be testing that battery for a local shop. So far i am quite impressed.

The reasons we want to push these through a tuning shop are these :
small
light
low self discharge

which is perfect for race cars application.

So far, 2 pros have been confirmed, and a 3rd one we didnt thought about.

Pros:
1/The car is starting way easier than it ever has before. Much less voltage sag than with a regular 30AH lead acid battery.
2/ That regular lead battery weighted around 20kgs . This one is 1.5kg. Thats 18.5kg LESS, and it is located in the extreme front right of the car. Removing weight here allows to recenter masses a bit, which is always a bonus.
3/ size : 10cmx 10cmx15cm. Previous one was 27cmx 22cm x 18 cm ... on that particular car, it allows to use the windscreen washing system again (for intercooler piping reasons, we need to use a smaller than stock battery, remove the washer bottle filler and push the battery where it is. This one allows the pipng AND the washer bottle filler to be used).


Now the cons. Bear in mind the battery was thought as a prototype, so it is there to find problems and cures. No real major flaws.

Cons :
1/ Cables get hot, i think they are a bit on the thin side. Not BURNING hot, but a bit too hot for my taste. While it is ok on my turbo, low compression 1.8L engine, it may not be ok for the 3.5L high compression V8 some of the shop customers use.

I need to inspect the connectors for heat damage. They dont look damaged, but i'd prefer to check, i am on the paranoïd side of things, esp. when it involves heat and current near alcohol based fuel and oil.


2/As of now, the casing is not waterproof. water/air can enter in holes for the wires. That may be a problem when driving under heavy rain (which i dont do but i tend to be extremely unlucky; and customers might want to use their car even under the rain ). A solution is to move the battery inside the car, but some competitions dont allow that.

This leads me to a question : can i seal it, or do these batteries need to vent ? I could add a fitting and a hose to a dryer zone if needed, but i wont if it is not. I could also use an external waterproof battery case and holder system, but i'd rather keep it simple.

3/Terminals. I have no problem hacking into the wiring of my junk/race car, but some people want a drop in solution, and they are not ok modifying their electrical circuit.


Solution to all 3 cons:
I think there is a way to solve all these cons: use 2 SAE terminals on top of the casing instead of a plug with cables going through. Using these allows people not to hack in their wiring, allows for a waterproof casing, removes 2 costy plugs, allows for shorter cable to be used (which could be made a bit thicker at the same time.

It would simplify a lot of things.

As far as the installation goes, i removed my battery connectors and made a waterproof junction box. I added an FIA cutoff switch (not kill switch) to easily disconnect the battery to avoid any drain. I may mod it to a kill switch later, it is not much to do.

I will investigate the heat problem and check balance this sunday. The car will have made approx ~20 starts so it will be a good time to check it.

So far, so good anyway. thanks go to ES people and Nancy from OSN :wink:

 

[SamTexas]

... 4S4P battery, A123 cells (approx 10AH)...

Are you referring to the green 2.3Ah 26650 A123 cells? Can you post a clear picture of that 4s4p battery?
What is the engine size of the car?

A solution is to move the battery inside the car,

Not a good solution under normal circumstances. A starter battery needs to be kept as close to the starter as possible to minimize voltage drop. You are already experiencing hot wires/cables. Moving the battery farther from the starter will exacerbate that problem.

 

[dogman dan]

FWIW, the cells only vent if there is a problem, so you can seal up any wire holes in your battery box.

Bigger wires to a connection block using normal battery terminals is not a bad idea, I'd just use a big lug and bolt terminal like the other end on normal battery cables. Screw using some expensive plug. Then you just need an insulated block to mount the lugs on.

 

[croustibat]

... 4S4P battery, A123 cells (approx 10AH)...

Are you referring to the green 2.3Ah 26650 A123 cells? Can you post a clear picture of that 4s4p battery?
What is the engine size of the car?

I think they are 26650 cells, but i did not check. I received the battery in a hard case and did not want to disassemble it. Now in the car, so i wont remove everything to make a pic. Engine is a 4 cylinders 1.8L turbo ( 8.5 to 9:1 compression, cant remember).

A solution is to move the battery inside the car,

Not a good solution under normal circumstances. A starter battery needs to be kept as close to the starter as possible to minimize voltage drop. You are already experiencing hot wires/cables. Moving the battery farther from the starter will exacerbate that problem.

Actually it would be a good solution on any rear wheel drive car, as the gearbox is just at the right of the driver (let hand drive), in the middle of the car. Putting the battery in allows shorter cables :wink:

Note: only the cables i got with the battery get hot. The other part of the system stays cool (but is something like 000 gauge, 10mm diameter; battery cables are gauge 2 or 3, approx 6mm)

 

[SamTexas]

Actually it would be a good solution on any rear wheel drive car, as the gearbox is just at the right of the driver (let hand drive), in the middle of the car. Putting the battery in allows shorter cables :wink:

On any rear wheel drive car? Not a chance. May be on YOUR rear wheel drive car but not ANY. I have plenty rear wheel drive cars. The engine on those cars is still in front and so is the starter. What does the gearbox have anything to do with the battery? The starter is the one drawing the highest current, so the battery needs to be as close to it as possible.