I'm working through some power/starting issues on my car which got me thinking about battery location. With a 3-5 lbs LifePo4 battery and with low gauge wire being so heavy it seems like I should move the battery out of the trunk and into the passenger area to reduce CG and keep total weight down. Any ideas where to put it and why?

Here's my current setup which someone wired for me ... too many long cables and not sure I like everything else hanging off the starter like that.

 

Since you already have changed your battery (i.e. no min weight to meet) why no locate it and the cutoff somewhere in the region of the starter (pass side floor).
The cutoff can be placed in the center console and a pull wire make it accessible for workers.
How thin wired you can use, I don't know, I'd be lazy and use the OEM ones (8G?).

I have thought about the Ballistic EVO2 12, but I'm balanced and at weight... In my friends Caterham it's another story

 

Passenger's side footwell seems ideal to me. It's extremely close to the starter and alternator, low and inside the wheel outline, and one of the best-protected ares (in terms of intrusion / deformation in a crash) in the entire car.

 

You could use something like a braille battery and put it under the front lip of the passenger seat. The battery would be on its side with the posts facing forward.

What is the factory battery weight?

.

 

Or you could buy a Deka and not pay a retarded ricer tax on a rebranded battery.

 

If the battery is as light as 3 lbs, it's probably worth moving all the way to the firewall simply to save the wire weight. Obviously as the weight goes up, the marginal cost of extra cables goes down.

The other obvious place is is behind the passenger seat, next to your elbow.

Don't forget: some sanctioning body's require a sealed box if you're battery is going to be in the passenger compartment.

donour

 

Anyone know the weight of the OEM battery? I'm currently using a motorcycle battery I grabbed from Autozone when my old one died, and I just went through what they had on the shelf and picked the lightest one. I think it's 10 lbs.

Relocating to the passenger footwell is an interesting idea.

-Ryan

 

~21 lb, depending.

EDIT: I think I'm going to go with an ETX9, which is ~ 7lb and $60. There's a huge thread on miataforum about light batteries: http://forum.miata.net/vb/showthread.php?t=323624

 

Duralast (Johnson Controls) quotes 24 lbs for their flooded 8AMU1R.

Westco and Federal (Deka) quote 25 lbs for the AGM version.

They're pretty light, as car batteries go.

 

Mike, put it in the passenger footwell. It allows the shortest cable runs (and thus shaves more weight).

 

Or you could both read the thread, as the OP already mentioned he's using a LiFePO4 which is significantly lighter than anything Braille/Deka makes.

 

The 12 Cell Ballistic LiFePO4 basically has the same cranking power as stock good life and weighs ~2.5 lbs. you could ditch 5lbs or more of wire by putting it in the engine compartment.

Bob

 

Remember, you are also drawing more amps then the normal Miata owner on startup. A trickle charger and jump pack handy might not be a bad idea. Whats your f/r weight and corner weights looking like? I will be following this, as my car is a pig.

 

Seeing as I wasn't replying to the OP..?

But I didn't know about this other brand, so thanks for that. Will look into it when I need a replacement.

 

One thing I have never been at all clear on... These LifePo4 batteries, are they actually capable of being charged normally by the alternator while the engine is running?

 

Apparently, or a large number of bikes would be stranded all over the place (Ballistic is used in a large number of HDs locally at least).

 

I would love to know how those batteries are configured internally. I have never been able to find any documentation whatsoever on how the BMS & Charge Controller are configured inside them. (Assuming they even contain one.)

The Ballistic batteries have a port on them for an external "BMS Balance Charger", which makes me question whether the battery itself contains any sort of electronics whatsoever. Whether anybody actually uses the balance charger on a regular basis is something I'd love to know.

Then there's the Braille offerings which, so far as I can tell, contain no external connections aside from the two main lugs.

And do none of these things contain an undervoltage protection circuit? Even LiFePO4 batteries tend to get pissed off when you drain them to below 2.8v / cell. (as in "No Soup For You!")

 

I'm pretty sure you get nothing but cells in these packs. The balance port is just hooking you up to groups of cells. Basically a big RC battery pack. Capacity is low (not so much an issue on a track car) compared to Pb. I don't leave the LiFe batteries in the car after an event for fear I'll forget to hit the cutoff and it will be dead in a few days. I have 35mA of dark current on my car.

Passenger footwell near the tunnel is probably where I'll put it. Or possibly on the tunnel behind the dash if I want to leave room for a passenger. The ECU is already there, the starter is about a foot away if you go through the tunnel, and there's a good place on the roll cage for the cutoff. Only the alternator has to go the distance. There's a cammed ls6 5.7L in the car with an aftermarket starter which is probably not working too well with 12+ feet of #6 wire if you count the ground. The engine bay would be an option if I didn't have a cutoff switch. I should probably check the voltage drop at the starter first, but I'm going to move the battery anyway ...

Haven't checked F/R and corner weights in a while. With a full NA 1.8L tank the F/R was 53/47.

I need to find a decent battery box that doesn't weigh more than the battery and isn't huge.

 

Fired up like a boss. No more flickering dash on startup. I was going to use #2 wire for the starter and battery, but it's heavy and doesn't look like I need it. Probably worth checking the voltage drop at the starter. I need to find a battery box that isn't huge and 3+ lbs.

 

Wow that is tiny..